First experienced this after marathon Civ one sessions on the Amiga. I was dreaming seeing those tiles move around the maps, building cities etc. When I woke up I felt sick and disorientated, a horrible feeling.
The "fun" one though was when I first got Mario Kart. I played it for hours and hours and hours. I resisted the inconvenience of hunger for as long as I could, but then to the kitchen I ran. When I went to go left to get the cutlery, I didn't turn to my left I "steered". When I went to go to the fridge on the right, I "steered" etc. Very odd sensation!