Hmm...
I'd go to the eye doctor and see if you need glasses.
I have to use glasses from time to time when I'm on the computer. Switching from my CRT monitor to an LCD helped greatly on me (although this part isn't so much a solution).
Glasses may make quite a bit of difference.
Another thing:
There is a theater in Indianapolis called the Cinedome, and although the experience was great, somehow, it made everyone in my family somewhat uneasy.
I couldn't get a good picture, but this theatre shown is basically the same:
The seats are exactly laid out like that; and the screen is shaped spherically.
It's very enveloping, but somehow, sickening.
With that example, I'm suggesting that your seating/position/head angle is not comfortable enough. Try sitting somewhere else, elevate (or lower) your seating position and try to get your head looking up or down more, depending on how you view when you get sick.
The other things; try playing a movie without subwoofer(s) on, and make sure the room is vented for a week or so (carpet and seating and other chemicals).