I don't normally have this problem but honestly, after playing any GTA game for any length of time I start to feel kind of like I have a hangover. I get a headache and feel kind of dizzy. It's even moreso with GTAIV because now I'm playing in HD on a big screen.
It's not that I can only play for 20 minutes or that I have to put the controller down at any point, but I can really only play for 3 hours or so at most and then afterwards I usually need to take some ibuprofen or something.
For me I don't think it's strictly motion sickness, although that may be part of it... it's also that the game to me just feels sort of dark and oppressive and it just gives me a headache. The graphics don't help, especially all the lighting effects - that bright washed-out sunlight going into dark rainy night, etc. I have fun playing it, but I've never really enjoyed that particular aspect of GTA games.
Edited by spacecadet, Fri May 2, 2008 9:51 AM.