Even yet, you might be sitting too close to the screen (because you are so entranced), or you are not drinking enough water.
Yeah I think this is the problem, I've been sitting quite close to the TV and I never really noticed... but funny thing is this does not happen when I play the PS2 on the same TV, seeing as my TV is not a flat screen but a big bulky TV it takes a lot of space in my room. I do get dizzy from some games, like star trek which you were a ship or something and you had to fly around endlessly shooting other ships that made me dizzy as hell, so I also think Motion Sickness could play a part in this, I've never been on a plane before so I didn't think of that either.
EDIT: I am going to replace the big TV with the smaller TV that I had previously because it seems that the TV is so big that it takes up space in my room, which makes it quite close to me even though I can't do anything about it wherever I sit. The problem with this is that I won't be able to play Hitman Blood Money which requires display setting to be set to PAL-60 and I can't do that with my small TV.