I too suffer from sleep paralysis. Had it about four times in my life now. Each time has folllowed a time of trauma... an operation, a break up etc. Each time equally as scarey. first time i thought my recently dead aunt was pulling the quilt off me from the bottom of the bed. I couldnt move - there was nothing there although it felt as though there was a presence in the room. The following three times, I have felt like a presence 'jump' onto the pillow beside me, as I was just awaking. Couldnt move a muscle or make a sound, but felt I could hear the breathing of something next to me, and felt a crushing feeling bearing down on my chest as though this 'thing' was holding me down. I also felt as though it was a bit difficult to breathe. In a few seconds I was able to move, and the 'thing' left my space and my room.
I am vaguely aware that it is the mind that wakes up a minute or so before the body, so the body is still in paralysis stage but the mind is awake. It is not that common and very frightening, but when you know what it is, you are less scared. Good luck with your research.