have you ever felt not very well (like, giddy) after playing a game? I noticed that it happens to me when there is a lot of movement. Earlier I though that its somehow related to fps, but now I doubt that fps is the only factor.
If you mean giddy as in tired, yeh I feel that way after about 4 hours of playing COD4. Intense stuff. I usually take a break to check forums, do some work, then afterwards I go on again.