Its a strange effect. I didn't notice it until AFTER I stopped playing the game. I had read something about that in an article, something about virtual reality type games that could make you sick like that. My symptoms were a slight nausea and instability/perception problems. Kinda weird. The mind gets used to the way things look in VR, then takes a while to adjust back to real life. Its called Simulator Sickness.
Sometimes bumping the refresh rate helps. I still get sick if I try to play older games, though. I recently reinstalled the original DOOM, and I get a headache if I try to play more than one level.