This one is pretty embarrassing.
So I'm deep, deep in REM sleep, happily dreaming away this morning... it's about 4.30am.
I start waking up because I can feel something on the back of my head (I think I'm on my side or stomach). Something is... Crawling On The Back Of My Head... near my neck, wandering around. It feels kind of big and I start worrying that it's going to go for my ear.
By now I'm awake but in total muscular paralysis... I can't move. The thing is still crawling... I spend another couple of minutes waiting for my body to regain control and wake up.
Finally it does and in a fit of panic I tried to do about three things at once; spin around and get up, run to the light to turn it on and brush whatever this thing is off my neck. I fail to do any of these and only proceed in falling straight down, out of bed and onto hard timber floors.
So there I am... on the floor, in the dark, flapping helplessly at the back of my head for an insect that is no longer there... but the time I can get up and turn the light on there's nothing to be seen. Looked everywhere; no insect. Then lost a couple of hours sleep, too freaked and in pain to fall asleep again... woke up with a grazed knee, very sore calf and sprained wrist.