It used to happen to me in the past. After playing for about 4 or 5 hours, and slightly. After almost 10 years of not playing fps games, I bought myself a copy of Half Life 2, and it hit me like a truck!
I can’t believe the strength of the nausea I experience after only 10 minutes of play. I wonder if it is specific to Half Life 2, or to my XPS’s monitor etc. The problem is trying to figure this out is expensive both in money and health terms. I guess I am really getting older. I have to lie down now, before I decorate the keyboard in a very unpleasant way!