Before the accident, Dad would sometimes emerge from a long sojourn on the toilet -- that most prosaic of locations -- with a faraway look in his eyes.
"Are you thinking about me?" my mother would tease.
"No, I'm thinking about science," Dad would reply, the opportunity to pay his wife of nearly 40 years a compliment completely escaping him.
My father, Tom Lyons, was a meteorologist and emeritus professor who helped establish Murdoch University's environmental science degree program and later its marine science degree program before retiring in 2014. Although I would query whether scientists ever truly retire.
Even during the summer holiday, including the days after Christmas when we indulged in our yearly ritual of watching the Australian men's cricket team play in the traditional Boxing Day Test match, he would periodically head toward the study to go and check on his model.
"You're lucky we know that's a mathematical model you're talking about, Dad," I would say.
In his mid-sixties, he was also annoyingly fit.
He cycled around the Canning River near his home in Perth, Australia, every morning, and four years earlier we'd walked the last 70 miles of one of Spain's famous Camino de Santiago pilgrims' routes together.
I elected to walk the Camino with Dad because I figured if I started complaining along the way about whose great idea it had been (mine), as my father he'd be morally obligated not to leave me behind.
It was also precious time to spend together now that I lived in a different city, despite our limited Spanish ("Dos Cola Cao, por favor") and differing views on siestas and sangria (I was pro both, Dad was opposed).
On the second-to-last day of our walk, I was trudging along with two painful blisters as he skipped ahead of me, declaring, "I could do another week of this!"
I feel annoyed when Mum's name flashes on my phone at breakfast. Doesn't she know how expensive it is to call internationally?
It's the second morning of a long-anticipated holiday in China I'm taking with a cousin and two other friends in September 2015. My cousin misses a call from her father, too, and we realize something has happened.
He texts: While on his morning bike ride, Dad was the victim of a hit-and-run and has been taken to the hospital.
In the lobby of my Beijing hotel, I fall apart and cling to my cousin. "I'm not ready to lose my father yet."
Worse still, I can't get a flight home until the following morning, which is how I find myself incongruously visiting the Great Wall of China on the afternoon of Dad's accident, while getting updates over the phone from my younger sister.
Two days later I'm standing by Dad's bed in the ICU, complaining to my sedated father that he hadn't warned me the Great Wall was so steep and that my calves are still killing me.
I find out later, during the court case for the driver who hit Dad, that he was struck head-on by a pickup truck that swerved onto the wrong side of the road.
The force of the collision ripped off the driver's side mirror and left Dad in a pool of blood by the side of the road having a seizure, his bike a tangled mess.
At Royal Perth Hospital, a skilled team of maxillofacial surgeons save the sight in his right eye, but as a result of the crash he has suffered a significant traumatic brain injury, or TBI.
A TBI is "an injury that involves some kind of blunt trauma to the head," says Jennie Ponsford, a professor of neuropsychology at Monash University and director of the Monash Epworth Rehabilitation Research Centre, both in Melbourne.
It can result from a bad fall, an assault or a car accident. A concussion is considered a mild traumatic brain injury. This distinguishes it from the broader category of acquired brain injuries, which can also be caused by vascular events like a stroke.
Research estimates that between 64 million and 74 million people globally suffer a TBI each year. According to the Centers for Disease Control and Prevention, a quarter of all TBIs in the US are caused by motor vehicle accidents.
With TBIs representing "the greatest contributor to death and disability globally among all trauma-related injuries," according to one study, many researchers have dubbed them a silent epidemic.
We used to think of a TBI as a single event, says Lyndsey Collins-Praino, an associate professor in translational neuroscience at the University of Adelaide.
"You had the injury, and then that was it," she says. "What we now know is that actually it's much more of a chronic disease process."
There is the primary injury, caused by the external force applied to the brain. This can bruise brain tissue, rupture blood vessels, damage neurons (or nerve cells) and shear axons, the long fibers that connect the neurons. This primary injury then kicks off a whole host of secondary cellular cascades, says Collins-Praino.
"Even those mild injuries [like concussion] can set off this sort of storm of events that's happening at the cellular level in the brain, which can lead to really negative long-term outcomes for people," she says.
The problem is, it's very hard to know at the outset whether a patient with a TBI will completely recover or have long-term impairments.
In the ICU, the doctors are reluctant to tell us what Dad might be like when he wakes up from sedation.
We dub one of them "Bad News Tim" because whenever he comes toward us it's to tell us something we don't want to hear. One of the nurses, Martin, plays gospel music to try to wake Dad up.
The next day I find out he's started to open his eyes for other people but he refuses to do so for me. So I get crafty.
"Da, if you don't open your eyes for me, Ashley [his nurse] and I will discuss last night's episode of The Bachelorette in excruciating detail."
I'm rewarded with a baleful glare through slitted lids. His hatred of reality TV remains intact.
After a week in intensive care, Dad is sent to the neuro ward. For weeks, he can't speak because of the tracheostomy to insert a tube to keep his airway open.
On a small whiteboard we're using to communicate with him, he laboriously points at the individual letters to spell out the words "I want to go home." I turn my head away to hide my tears.
I don't like how some of the staff infantilize him, speaking to him like they're speaking to a young child rather than an esteemed scientist because he can't communicate easily.
Instead I keep cracking jokes with him like we used to, about silly things like the superiority of the state of Western Australia (where we are) to the state of Victoria (where Dad was born) or how our respective teams are doing in cricket.
When I land a particularly well-timed gibe, I get a sarcastic finger point of his left index finger. It's so early in his recovery we still don't know how much the injury has impacted his cognition, but his finger jab at least tells us some parts of his personality remain intact.
One of the biggest things people don't understand about TBIs, the experts tell me, is how long it can take for someone to recover. "It's not just a matter of having the injury and then shaking it off," Collins-Praino says.
Explains Dr. Kathleen McCarthy, a rehabilitation medicine physician in private practice in Sydney, "It's a long, grueling rehab for the more severe people." Like the other medical experts I interviewed, she wasn't involved in Dad's care.
McCarthy has followed most patients with severe brain injuries for about three to five years, but she's also looked after patients for 20.
The upside is that all brain injuries improve, she says, noting that while the degree of improvement is hard to predict, every brain will continue to get better over time.
A couple of months after Dad's accident, a friend assumes he must be home from the hospital by now. He's not.
After six weeks at Royal Perth Hospital, he's transferred to the State Rehabilitation Service, where he spends the next three and a half months in rehab.
He works with a range of medical specialists, including physiotherapists and occupational therapists, to improve his mobility and other medical issues to the point where he's well enough to continue his rehabilitation at home.
For Christmas 2015, three months after the accident, we're lucky we're allowed to bring him home for the day.
People react differently to Dad's injury. I'm hurt by a former housemate who's met Dad on multiple occasions, but who can no longer use the word "father" with me in conversation. But I'm so grateful for the friend who tells me to call whenever I need to have a good cry.
McCarthy isn't surprised some people find talking to me about Dad too confronting.
"Most people feel inadequate," she says. "They're problem solvers, and it's not a problem to solve."
We're experiencing a type of "ambiguous loss" with Dad's brain injury. He's still physically with us, but psychologically he's altered and at times absent. There are no clearly defined rituals to guide people on how to respond to that.
His other physical injuries will heal or reach a point of stasis, but his TBI is more elusive. Sometimes he responds to something the way he used to do, other times we're forcefully reminded we're dealing with someone who has brain damage.
There are also lighter moments watching a scientist go through rehab, particularly given my own background as a science writer.
If you had asked me to imagine my father's brain before the accident, it wouldn't be as a mass of jelly-like tissue curled serpentine inside his skull, but as a three-dimensional web of light, constantly changing as electrical signals dart around his mind.
This was a man who used to fly in motorized gliders roughly 30 to 60 feet above the tree canopy to collect meteorological data for his research looking at why there was 20% less rainfall on the agricultural side compared to the native vegetation side of Western Australia's Rabbit Proof Fence. He'd tease his American collaborators about the threat of drop bears and hoop snakes in the remote West Australian town of Lake King.
Dad's occupational therapist is surprised when he uses logic to reassemble wooden blocks into the shape of a triangle.
"I've never seen anyone do it that way before," Catherine says.
The scientist and his scientifically minded daughter look at her uncomprehendingly. Isn't it obvious people would try to solve the puzzle that way?
TBIs are often referred to as invisible injuries because only about 20% of the most severe injuries cause physical deficits, McCarthy says.
"For a lot of people, if you look at them, they seem normal. ... It's invisible to people on first impression."
The most common consequences of TBIs are cognitive and behavioral changes, Ponsford says. Fatigue, memory problems and irritability have all been associated with brain injuries.
A lot of people with TBIs interviewed by Ponsford say having a hidden disability can be a barrier when interacting with others.
One of the problems with brain injuries, McCarthy says, is that if you're down a minute amount in terms of your cognition, you know it at once. Whereas you may not notice a much larger problem with your mobility.
According to the Australian Bureau of Statistics' 2018 Survey of Disability, Aging and Careers, 1,459,200 Australians reported having a head injury, stroke or other acquired brain injury. Of those, 323,200 people have a disability, meaning their acquired brain injury restricts their everyday activities.
Statistics from the US CDC suggest that 2.5 million Americans visit an emergency department due wholly or partly to a TBI every year, and between 3.2 million and 5.3 million people live with a TBI-related disability.
After almost five months in rehab, Dad finally comes home.
Unfortunately, he's part of the 20% of TBI sufferers with physical problems, including needing to relearn how to walk. For someone used to being so active, it's a critical initial step in his recovery.
This fixation on walking is something McCarthy has seen again and again.
"People almost totally exclude any other thinking, except for walking," she says. "They want to walk, they have to walk, it must be so inbuilt."
At first, Dad appears to be improving, walking carefully but confidently the short distance between a chair in the family room and a chair in the dining room. A couple of weeks later, things start going wrong again.
He gets sick, he's not as mobile, his left leg is swollen and he becomes delirious. Mum has to call an ambulance to take him to hospital with a urinary tract infection and a likely deep vein thrombosis (DVT), or blood clot.
From my home in a small West Australian regional town I once again drop everything and travel to Perth to see him. I'm too upset to drive the five hours home, so a friend drops me off at the small airport outside town instead.
Dad is diminished.
He's a little old man sitting in a big hospital bed, stooped and frail, not the man I always looked up to and said I would grow taller than by genetics or stilettos.
His stay at his third hospital in six months also affects Dad's mood.
Before the accident, he was someone with an unfailingly positive point of view, who enjoyed being active and exploring the world around him. Now he's more closed in on himself, vulnerable and scared.
One day, he tells me he doesn't want to be a human anymore.
I try to make light of his comment.
"Well, I think you've left it too late to become a dog," I say.
He blinks at me, surprised.
"Once someone starts to get insight or self-awareness, then often they become quite depressed, because that's when they start to realize that they're different," McCarthy says.
"They're not the same as they used to be."
While no two TBIs are alike, they lead to some common problems.
Fatigue is frequently seen across the spectrum of injury severity, Monash neuropsychologist Ponsford says, and that's due to many factors.
"People have diffuse axonal injuries in their brains, diffuse neuronal injury, which means they've sort of got less horsepower, they've got fewer neuronal connections," she says.
People with TBIs also commonly have sleep problems, including sleep apnea, contributing to their fatigue. Dad doesn't get the same benefit from a good night's sleep as he did before the accident, and when he's tired he starts to slur his speech.
Cognitively, there may be changes in memory, the ability to concentrate and the speed at which patients can think or process information.
Once an avid reader of both scientific literature and historical epics, Dad now struggles to read as his difficulty concentrating no longer makes it pleasurable.
Then there are the so-called executive functions, Ponsford says, which incorporate the ability to plan and organize, to set goals and follow through on them, to monitor your behavior and thought processes. These functions are governed by the frontal lobes of the brain -- Dad's right frontal lobe bore the brunt of his injury.
He becomes hopeless at replying to even a simple text message as he forgets to do so.
McCarthy describes the frontal lobes as the putting-it-all-together part of the brain.
"It's like the conductor of an orchestra," she explains.
Executive functions then morph into control over behavior. Some people with TBIs may get more easily frustrated, irritable or aggressive. A lot of people become disinhibited: tending to talk too much, frequently swearing or not monitoring what's coming out of their mouths very well but saying whatever's in their head.
"If you're [working] in brain injury, you just really ignore the swearing," McCarthy says. Luckily for my mother, who loathes swearing, that hasn't happened in my father's case.
"There's often an inflexibility of thinking, difficulty thinking in abstract terms, generalizing from a single instance and understanding other people's point of view, reading other people's emotions," Ponsford says.
I notice this when I'm speaking to Dad over the phone. He will laugh when I'm relating a funny story to him, and then respond in exactly the same way when I'm telling him about something serious.
Dad is elated when we're able to bring him home from the hospital again, smiling like a delighted child who can't quite believe his luck.
As the months pass I notice two significant changes in my father.
He was always quick with a witty remark or playful banter, including his much proclaimed promise to live long enough to be a problem to his children. Now he rarely is able to make jokes anymore.
Humor is linked with the ability to think in abstract terms, Ponsford tells me, and Dad's ability to draw an inference has been affected.
But sometimes he surprises me. One such time I'm kneeling in front of him, helping him put on his shoe.
"Ouch!" he says.
"What's happened?" I say, instantly concerned and protective the way you are with someone you now perceive as fragile.
I look up to see a cheeky grin: "Gotcha."
"You bastard!" I reply.
As a result of his injury, it feels like Dad has turned inward. While never an effusive person, he cannot now express affection, either through words of endearment or the little things he used to do to take care of us, like bringing me a freshly brewed cup of tea every morning when I was visiting home.
"Bye, Dad. Love you," I say at the end of a phone conversation.
Ponsford says it doesn't necessarily mean he's not feeling emotions, it's more that there's a certain passivity with expressing them.
Some people with TBIs, she says, go in the opposite direction, excessively expressing emotions out of all proportion to what they're actually feeling, like laughing or crying for no apparent reason.
I miss hearing Dad saying a reassuring "God bless" at the end of a phone call.
Dad's injury profoundly impacts us as a family, but we all cope in different ways.
It's hardest on Mum, whose decades-long relationship with Dad has been irrevocably altered.
Although she gets daily help from disability support workers, she's been thrust into the role of Dad's primary caregiver at a time when, with Dad now retired, they were looking at being able to take things a bit easier.
Dad was indulging his love of cooking and had taken over making dinner every night, and they were planning on finally going for a holiday traveling Victoria's Great Ocean Road, a trip Dad had been promising to take Mum on for most of their marriage.
She's also in many ways lost her companion and teammate of the last 40 years. The person who took care of her, sometimes gently pushing her to try things outside her comfort zone. The person she took care of, encouraging him to be a bit more extroverted, is now forever changed.
I have to remind Dad of birthdays, anniversaries and other occasions of note, then cajole him to write more in the card than "Thank you for taking care of me."
My sister prefers to think of Dad as gone, with this new man having taken his place.
I look for ways that Dad and I can still do things together that we've always enjoyed, like going to cricket matches or watching a science fiction film or television show together, like Doctor Who.
I try to respond to his medical tribulations with humor. I am upbeat on the phone when he gets another DVT.
"Well, at least they didn't want to cut off your leg," I say.
"You always see the positive side of things," he says, half grumbling at me.
In another phone call with my sister I burst into tears.
I tell a counselor who specializes in helping people impacted by road accidents that I always imagined that if something this terrible were to happen to my family I would behave like a living saint, selfless and calm under pressure.
"And how's that going for you?" she asks, openly laughing at me.
"Not well," I reply tersely.
Sometimes I find myself walking around my house, crying ugly, angry tears that something this cruel could happen to my wonderful and kind father, a man who would think of nothing of flying across the country to help me move cities yet again, or once drove me some 250 miles and cheerfully caught the bus back to Perth the next day because he could see I was too tired to drive home by myself.
TBIs can have a devastating impact on family members, Ponsford says.
"If you're in a close relationship with a person as a spouse or partner, that person may be just a different person, and they're not sensitive to your emotions in the same way that they were."
Families as a whole can become socially isolated, Ponsford says, because they're managing their loved one's injury and other people don't understand the multiple stresses involved.
One way families can become more resilient is by becoming a little bit more independent, according to McCarthy, the rehabilitation medicine physician from Sydney.
"I get dictatorial to people and say you have to look after yourself. It's no good if you run yourself into the ground, it's not going to help [your loved one]," she says.
The brain has some capacity for reorganization and regeneration, Ponsford says, although the capacity for neurons to regrow is limited.
"It's thought that the so-called recovery that people experience is probably more a reorganization within the brain, and quite a lot of intact areas taking over impaired functions," she says. "Also people learn to do things in new ways, they adapt."
However, there are some factors that influence how well you recover from a TBI.
The older you are when you sustain the injury does result in greater initial consequences on your cognition and function, although Ponsford's research doesn't suggest it causes greater decline over time.
The higher your IQ before your injury, the better.
A neuropsychologist tells Dad he now has more of an average brain since his accident. But Dad gets upset that he can't do sudoku puzzles as quickly as he used to.
A friend laughs when I tell her this: "Suzannah, I can't do sudoku puzzles, and I don't have a brain injury."
It's like any brain function, McCarthy says. The more he does it, the better he'll get.
What treatments are available to you, as well as the environment around you, can also impact how well you do. For example, having a wheelchair so you're mobile if you can't walk, stable accommodation and being able to buy decent food all help you to do better.
Ponsford says it's important people get access to both psychological and physical help, as someone's coping style has a bigger impact on their long-term recovery than anything else.
"Having access to the right types of support at the right time is very important," she says.
Dad takes up hippotherapy, a type of assisted horse-riding therapy, to help improve his walking, but is not amused when I tell him he reminds me of the classic Old Spice ad.
A TBI sometimes feels like an injury that keeps on giving -- in the worst possible way. Just when you think you've reached peak shit, another layer reveals itself to you.
That moment comes for us nearly two years after Dad's accident.
He's diagnosed with a rare neurodegenerative condition, hypertrophic olivary degeneration, thought to have been brought on by his TBI.
It affects his walking and balance, which explains why he's still so wobbly on his feet. It also impacts his soft palate, causing him to sometimes choke when he drinks something too quickly.
When we consult a second neurologist, he tells us Dad's balance is shot and there's nothing he can do about it.
"Across the board for neurodegenerative conditions, we know that trauma can be a contributing factor," Collins-Praino says.
In large part, that's likely due to the neuroinflammation that gets set off by the primary injury, she says.
Her research is looking at how to better predict whether someone with a TBI will recover, is at risk of long-lasting impairments or will go on to develop a neurodegenerative condition.
"We need to know who's most at risk … so that we can intervene and get people the support and programs that will help them to prevent those outcomes," Collins-Praino says.
We've stopped hoping the next specialist will be the one that proposes the miracle cure, or helps Dad walk properly again. As each medical procedure brings new indignities, I wonder how much more he can take.
There are still moments of joy, however.
In the leadup to my sister's wedding three and half years after the accident, Dad drafts his father-of-the-bride speech.
I have to nearly completely rewrite it, after removing all the parts Dad thought would be funny but could end up insulting half the audience.
He goes off script a couple of times, but not so rogue that I have to take away the mic, and I'm pleased he feels comfortable enough to ad lib.
The speech is a huge success. People come up afterward to tell him he made them cry. Especially the line where he thanked his new son-in-law for being there for his daughter at a time of great distress for our family.
Many people with very severe brain injuries go on to lead essentially normal lives, Ponsford says. She's interviewed people with TBIs up to 30 years after their injury.
Her research shows that while initially people feel very negative and have many negative experiences due to their TBI, over time they often reach a level of acceptance.
"Almost all of them were able to find something positive in the experience, which was marked," she says. "I think it takes more than a decade to reach that point."
We don't reach that fabled decade with Dad.
Five and a half years after the accident, in April 2021, my father dies suddenly at age 72 during one of the frequent hospital visits that were beginning to feel almost routine.
Despite the huge presence he is in my life, and in our family, the time has come for us to let him go.
Now living on the other side of the country, I watch over FaceTime as his wasted body takes its last, labored, rattling breaths.
Learning to live with my father's brain injury was about both him and us accepting the person he had become, rather than comparing him with how he was before.
"Finding out the new person and working out what the person can do … and what they have to give, and their enjoyment of life, is really what rehabilitation's all about," Ponsford says.
There were days when everything went wrong: Dad would have another bad choking episode or a fall. There were days he told me he didn't want to be a human anymore.
Just like there were days I took him to a cricket match and bought him a beer and hot chips (with an admonishment not to tell Mum) like he used to do for me.
But at my sister's wedding, a wonderful thing happens. Toward the end of the night one of her friends wheels Dad in his chair into the middle of a crowd on the dance floor.
And just for this moment, my Dad, who I've never seen dance in my life, is smiling with his head tossed back, having a boogie.
Suzannah Lyons is a freelance science journalist who worked for the Australian Broadcasting Corporation for over a decade. She trained as a chemist but found she was better at telling stories than hanging out in the lab. She can still make a mean batch of cornflour slime. Follow her on Twitter @ZtheTrain.