I've heard about the old hag and the incubus/succubus or whicherver it is that sits on you while trapped in a sort of sleep paralysis long before I've found myself actually in sleep paralysis. I think I've been in sleep paralysis a couple of times, and I did have a visitation by some sort of being... but I would not say it was a malicious entity.

THE FIRST TIME: I had an OOBE for the first and only time, and I was wandering throughout my house for a short period. I know I it was an OOBE because I felt all of the strange vibrations and noises that I have since read about when people astral project or have OOBE's. Anyhow, shortly upon re-entering my body, I looked to my bedside and saw a large almost heroic silouette of a person. I say "heroic" because it was a dark silouette but there were great shafts of white light emenating from within this being's body. This being spoke to me with some form of telepathy I think, and told me basically "this is what becomes of people who pollute their bodies with intoxicants." Then I felt the painful constriction in my chest that people describe when speaking of the old hag or whatever. I somehow forced myself to "wake up" from that experience.

THE SECOND TIME: This time I was much more calm and relaxed. I was sleeping over a friends house and I was totally covered in blankets. When I entered the paralysis I knew I couldn't move, but I knew if I relaxed and just "rolled with it" I would be fine. I remember seeing a view from inside the blankets in which I laid, but what saw was very different from what it looked like in real life... it was almost like an alternate version of where I was. There weren't any colors really, and there were strange wormlike fibers on the blankets wriggling around. It was weired, but I guess the point is that since I was relaxed there was no painful constriction and I soon ventured from there into a non-lucid dream.

I guess I thought it was kind of interesting that the first time I had the sleep paralysis and painfull suffocating, I saw a kind of "higher" being enflicting the pain rather than the evil hag or something like that.