I move around a lot when I sleep. It could be the fact that I'm usually engaged in a riveting alien invasion/apocalypse driven plot line in my dream world. When I was a kid, I had a bunk bed and would sometimes wake up in the morning on the top bunk. I've been known to kick people out of bed, snore, sleep talk, and who knows what else. You could say I'm a pretty big bastard in the R.E.M. state.
David Ichioka did a series of interesting time-lapse pictures of different people sleeping. Worth a look. Check it out HERE.