Something Sitting or Laying on My Back

Sometimes at night I will go into sleep paralysis and I'll be on my stomach. I remember a few times it happened I felt something on my back holding me down. So one night I decided to relax when i went into sleep paralysis when I was on my stomach and I was trying to see if I could feel anything moving. I felt the covers moving slightly from my legs up to my back so I guess whatever it was it was crawling up from the end of my bed. I never ever open my eyes whenever this happens because I'm afraid to see what is there. My head was turned towards the wall so i decided to open my eyes just a little. When i did I saw a black hand like a shadow next to my hand. Either it was that or it was holding down my hand, but I can't remember. Right when I opened my eyes whatever was on my back made this weird growling noise. It really scared me so I shut my eyes again and tried to get myself to wake up.