I would have to agree its related to your astral body preparing for sleep.

I have had the sensation of spinning whilst falling asleep multiple times although it occurs randomly. I find it to be quite a pleasant experience and have learnt how to manipulate it so I can speed up or slow down the spinning sensation. I feel it as my astral body and have some experience with astral projection which is why I believe it's my astral body spinning and not mental hallucination or delusion.

I have yet to learn how to turn this sensation into a direct astral projection experience, although there have been times when I have fallen asleep afterwards and entered AP.

I used to have this a lot as a kid, sort of. I used to feel (almost every night) that I was rotating as though on an axis and was filled with an incredible sense of vertigo, and whenever it got to the point where it felt I was going to be "tipped off" the bed it always reset back to the usual position in my mind.

Sometimes I still get it, though nowhere near to the extent I did when I was younger. I also suffer from insomnia.

This happens to me...so much. More so on the somersaulting bit when I was a little kid, but my bed still shakes from time to time. Very gently, but its still noticeable.

I never knew it could be astral projection. I'm kind of wary to try it though -- I've read in various places that entities can enter your body and take control while you're out of it.