I assume that the video appears to be playing at high speed.
Sounds like you are recording in "Time Lapse" mode.
Which would take one image each second, or something similar.
Check page 83 in the User Manual.
i started having the next problem in the last week.
when i play a movie after i record it or while playing it on the computer the movie speed is very big.
for example I record 40 seconds movie clip and when i play on the camera its end-to-end in 1-2 seconds. same as playing on the computer.
i have tried to "reset" the camera and browsing for hour on the Internet but could not find any similar problem,