I think this is a possibility, but for the vast majority of people it's simply consciously falling asleep into a dream state. Since you are aware, you are lucid dreaming. Look it up if you're not familiar with it. This is what's happening. You are in a dream that feels real because you are fully aware and in control of your surroundings. Have you ever been in a dream, and all of a sudden realized you were dreaming? Even though you knew you were dreaming, it feels as if you are in the real world. Then you wished to be awake, and you immediately woke up? That's not to say you can't have psychic experiences while dreaming... The point is, at least for most people, your spirit does not leave the body.