In my view it is something like half-dream. It happened to me circa five times. The principle of this phenomenon is, that you are feeling physical body(paralysed), but you think, that you are in a dream. You are in subconsciousness with full visualization of everything in a dream and other aspects of dream, but you feel physical body and you are lying on a physical bed. Sometimes I am lying on a bed in a dream and I want to pick up my head, but it is impossible. I wake up and I notice, that I was trying to pick up my real physical head. (because I can feel this fact on my neck) That induce, that I had connected my dreaming mind to phycisal nerves on a physical body.