The accepted term for that particular variety of motion sickness has been called "simulator sickness" ...

It doesn't affect just video-game players. A 1995 report by the U.S. Army Research Institute found that almost half the military pilots who used flight simulators developed aftereffects — and 10 percent of those respondents had symptoms lasting more than 4 hours.

How can you fix it? You might try sitting farther away from the screen so that it doesn't fill your field of vision. Also, experience often helps you get over it. It seems that after enough exposure to dizzying graphics, your brain learns that you don't die from poison every time you play a first- person shooter, and it lets you enjoy your fun.

- Popular Mechanics, "Videogame Motion Sickness: Tech Clinic Diagnosis," Aug. 2007.