This has happened to me hundreds of times throughout my whole life! It didn't realize it was so common until reading throughout this thread. It just happened last week while I was in bed with my lady. It's like I'm half awake and can see everything like my clock which is the actual time. I'll be trying to yell help, but I'm paralized and something is hovering above me forcing me down. My lady says that I just always mumble in my sleep after I ask her what I was doing. So last week when I knew it started to happen, I started banging the wall with my arm and my lady woke me up. It use to scare the shit out of me, but now I'm use to it. Religious folks have told me in the past that it's evil spirits. They also mentioned that these spirits only like it when it is dark or very dark places. They always said to try and yell "YHWH" (Yahweh) which is god's name in Hebrew or translated "Jehovah" in English when they attack you in your sleep.
Anyway, if anyone is reading this tonight, I wouldn't recommend going to sleep until daylight, lol.