When I was young I got SP all the time. It scared me beyond belief back then. It's like you feel a presence and just know you cant move. Once I was on my stomach and some kind of tree monster with the face of a dead dog started strangling me in this state, I cant sleep on my stomach to this day and I'm 25. I spent years avoiding the felling of oncoming sp until i realised in an 8th grade science class that this state is the steeping stone to lucid dreams, so I spent years trying to no end to bring the state back. and I cant.