I can play games for hours on end. No problems. Good friend of mine, though, there are certain genres -- FPS and driving mainly -- that make him physically sick.
He's not alone. It's a safe bet most of you either know someone, or suffer yourself, from motion sickness brought on by video games.
There's a great piece on The Guardian's website exploring the subject, noting that while there's been little hard science done on it, it's estimated between 10-50% of people may experience motion sickness while gaming to some degree.
Noting that US research on military flight simulators found around half of users reported some kind of sickness after use, it's speculated that it's caused in video gaming by a disconnect between your eyes detecting motion on the screen while your inner ear has no such luck (because, you know, you're not actually moving).
This might trick your body into thinking it's being poisoned, which triggers a nausea reflex.
So how do you fix the problem? Well, there's no cure, but as The Guardian's helpful test subject notes, over-the-counter motion sickness medication (he cites Joy-Rides) can either delay or alleviate the effects slightly.
Playing video games makes me sick [The Guardian]