depends who you ask, in science- they still studying about this condition, but in religion all over the world, there was three types of sleep paralyze or more first is, a old hag name kuku who just love to go on the top of you bind you with her crazy powers and stuff, and strugle you and make you pee in your pants from being scared just for fun.. but also there was some old folks who bilieved that she was the angel of death she somehow warning you that you might die from someone or something, but then again they said she could take someones soul and drag it to the gates of hell, like they were saying she wants your soul so she would let you live until the momment when you died the way she wants you to die.
2. The old hag was an alien, who just love to torture you like that.
3. Shadow peoples, they everywhere some of them are good some of them are bad and some of them are really really bad they usually men, and they said the worst are the shadow people with hats, but some of people bilieve that there was another type of shadow people a woman and she is the old hag