This strung to mind with the Out Of Body experience and Sys quoting "hypnagogic jerk"
I find this a Interesting point, Because this has happened to me many times.
But something i Do notice when it happens, its normally in a dream and you Trip up or fall and you kinda Jump / Jerk in the motion.
So is your body moved to the action of your dream? or is this your dream moving to the motion of your body!
But lets look at something else.
If your dreaming then the surroundings of you is involved in the dream.
Noses, lighting, effects on your body.
If your dreaming and someone tickles your feet! this becomes part of your dream, But if your dreaming of walking in New York you dont just switch to a point where someone is tickling your feet.
I use this as an example as it has happened to me, but the dream involved a Full body massage, and my feet being massaged,
But in fact i was being tickled on my feet while i was asleep.
So is the brain already 10 steps ahead and set the scene for this action on your body?
Does anyone follow what am saying or do i sound crazy

Or at least sort of understand what am trying to get across