I have experienced SP since about 15years old,although haven't had one in the last 2/3 years. I think, because they scared me so much, that i learned how to stop them, and now i know more about SP,cannot start them up again.
Apart from the terrifying physical symptoms, unable to breathe properly ect, i never experienced frightening entites and such. I never felt there was anyone else in the room either.
Once i thought i was up against the ceiling and, another time, saw my mother walk in and sit on the bed, although she was transparent,and i knew her to be downstairs at the time.