[yupmat]

I too have wondered this! In fact, Doom 1 was the only game to ever make me throw up (9 or 10 years old at the time). Despite playing all kinds of games comfortably, Half-Life 2 makes me nauseated.

For some reason I've associated the sounds of those games to the sick feeling. I've always wondered if the sound has anything to do with it OR if my brain is just reminded by the sounds and is trying to warn me "I've been sick here".

[ZeikJT]

I would assume your latter conclusion is probably right, but the former would be more interesting!