Wow, I used to do that all the time and I totally stopped. I don't know why I stopped, I just did. The way I learned is I used to meditate a lot before I started smoking and I would feel the world and energy around me and bring it in by sitting up straight and breathing deeply. It's great practice for the mind soul and body. I would sit up straight and anytime my head would fall around, I'd wake up. Kinda like what Euphoric was saying with the arm thing. You can't really have any instructions on how to do this.. you just have to be open-minded and relaxed and feel your way out of your body... if that makes sense.