I get motion sickness in various degrees playing FPS games, depending on the camera angle the game uses and how fast paced the game is. A long time ago when Team Fortress was popular, I was playing and would continually get sick.. headache, nausia, etc. One night I was like, this is so stupid, it's an F'in game. So I played beyond the point my body said to stop. One hour later, I felt worse then I've ever felt in my life! I had an unbelievable headache that no amount of tylenol could cure, had to lay down with ice across my eyes and forehead for about 5 hours. If you feel sick from playing games, this is a normal response, just as riding in the back of the bus is for some. Stop when your body tells you it's time, I'm sure this is how videogames kill others.
-csa