I was having a nightmare. Gremlins were chasing me around an old house. I awoke from the terror. But, although my eyes were open, I couldn’t move. This was more terrifying than my nightmare. It got worse. A small creature – one of the gremlins? – was sitting on a bookcase looking at me. The creature faded away from my sight and I could move my muscles.
I was drifting off to sleep, but still moving in and out of consciousness. I came out of sleep one more time and opened my eyes. There, just inches from my own face, was the face of an old, terrifying woman. She faded from my sight.
I awoke in my bedroom. I was afraid and could not move. I heard two quick clicks in my closet. Then I heard them in the opposite corner of the room. Then they came from the other side again, but closer to me. The clicks went back and forth until the appeared just beside my ears. At that point, I could scream and jumped up. The clicking was gone.
The above were examples of hypnopompic sleep paralysis. Most of the muscles attached to our skeleton go paralyzed while we sleep. If they didn’t, we’d act out our dreams and probably hurt ourselves and others, not to mention not get a very restful sleep. But sometimes we can awaken before the muscular paralysis wears off.
For some reason, when this happens, people experience terror and see frightening beings. Some folks argue that this phenomenon is the source of old stories of succubi and new stories of alien abduction. From my own experience, I can see how this could be. I have yet to read of anyone else having auditory hallucinations like I did in my third example, but there it is.