on my phone during my commute to work and the duration is only for an hour or less, but never being dizzy afterwards.
Maybe your eyes are straining from reading smaller fonts or even possibly of poor lighting?
Maybe it's CVS: http://www.aoa.org/patients-and-public/caring-for-your-vision/protecting-your-vision/computer-vision-syndrome?sso=y
I'd recommend taking frequent breaks or if you can help it, just don't use the tablet for the entire day? I personally believe that anything you do, even healthy stuff, when it is excessively done, it can be harmful to your health.
I hope this helps a bit, but this can prevented by giving your eyes some rest.
Cheers,
-Lee
What kind of damage could it possibly be?
This totally sucks

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic