Use to get it all the time, bought a pillow that doesn't let me roll onto my back.
I use to be in the sleep state and walk around eyes wide open, now that was freaky.
Worst experience just moved into a brand new apartment, was really tired so I passed out on the sofa that night, I woke up0 frozen and saw and felt this
invisible outline of a creature coming towards me and jumped on me and started to strangle me, actually fell to the floor and started wrestling with it, whe I came too screaming at the top of my lungs, my heart felt like it was going to come out of my chest, it was the weirdest feeling imagine being the most frightened to you can ever get then go up one level from that, it was unreal. Doesn't help either the huge apartment complex use to be a nursing home, where old people died all the time.
What's weird if you look up on the web, a lot of people around the world have had about the same thing happen to them.