Why do i feel weird at movie theaters?

Whenever I go to a movie and see it late, like a 10PM showing, or a Midnight showing, I can't focus on the screen, its like my brain can't recognize the film, and then I start getting anxiety, and I feel like I'm gunna barf. So now I'm outside of the theater waiting for my movie to end while I'm writing this. (Transformers premire) and my friends are having a blast, while I'm here feeling sick and lightheaded. I'm just wondering why this happens? Thanks for your help(: