I recently broke a Halo addiction, during which I dreamed about Halo nearly every night for a few weeks. I had the same experience as you describe several times, where I was both seeing the game as if I was in it, and yet I could feel myself playing. It probably has something to do with the fact that we're so used to experiencing the game from a certain point of view that even when the pov changes, some of what we're used to remain. If that made sense... I've also had experiences where, as I'm falling asleep, I'll be thinking about playing a console game, and I start moving my hands as if I was actually playing. Probably a similar reason: thats our expected method of input in that environment.