I do that too. I'm a gamer and computer geek though, so it's normal for me. For me though I go cross eyed and have to strain to get myself to focus for a while. Then it stops. Maybe something to do with the lights of it too, how as you're surfing the net or playing video games there are a lot of lights that change or change position or something? I think it freaks out some people and induces siezures, maybe it freaks out some people's eyes?

Maybe I'm wierd though.