Sleep paralysis is a very interesting phenomena. The paralysis part is normal. It keeps you from actually doing all the things that you dream yourself doing. But when you wake in that state, it seems often that you experience things that are very different from ordinary reality, and yet you won't feel a "waking up" from that experience -- you are already awake! I used to suffer from it when I was younger, but most of them seemed to revolve around a certain set of events. So my experience of it leads me to suspect it isn't always the thing the simple medical explanation would have us believe. But other times leave me mystified to explain it.
For instance, the last time I experienced sleep paralysis, I clearly heard small footsteps cross the carpet in my bedroom until they stopped right next to my left ear, and then a voice started chanting, "Baby! baby! baby!" in an excited, troll-like voice. A very odd thing! It slowly faded off into the distance, and then silence when I started praying, but I never had the sensation of waking, I just gradually got control of my limbs.
A very bizarre thing, but what does it mean? If it is my "unconscious mind" trying to tell me something, what? If something not part of my mind, double what?