Well, I'll tell you my experiences, so what I'm talking about:
Several years ago I was an avid player of Counter Strike. And what happened to me? One day during holidays, maybe after 4 hours of gaming, I went from my house, and when I was passing the corner of wall, I instinctively suspiciously looked over the corner, like terrorist should have been there. Like ingame.
Yesterday, I was playing Warrock several hours, and spent a lot of time in helicopters (you know, Im getting used to flying in them). And now I just noticed that my vision is somehow being pulled to side now and then.. like the helicopter rolling to the side.
Have you ever encountered something like that?