This experience used to happen to me a lot. I think, but don't know, that it is a natural occurance. It happens sometimes when I meditate or when I am completely relaxed, some kind of seperation of the mind from the body.

I do know that this only happens when I am relaxed and I haven't been able to relax for quite some time.

I don't think it is anything to be concerned about. When I was a kid I used to try to make it happen, it was fun and difficult to accomplish.