I have had this many times and it can be terryfying, I would use a stronger word but there's not ne out there to describe it. It's sleep paralysis my friend. It can seem so real. Let me also say my SP comes on as I wake in the night and then I seem to be sucked into a vortex, the next minute I'm in my bed with this ghostly apparition attacking me, and I mean biting me etc and last time it happened it spoke to me for the first time ever and said "I will get you eventually, get out the fuckin duvet" then it bit my stomache. I woke in a blind sweat because even in normal dreams I sense it's presence, it's absolutely horrendous. When it happens again don't try to fight it, calm yourself and focus. Repeat to yourself "this is my dream and I'm in control" then ask it to "please leave". Trust me it works but it may take you a few times to manage to calm yourself enough. PM me anytime and ill help you with this. Good luck