Lie on your stomach, with your arms over your head (i.e. stretched out along the floor). Have a friend lift your forearms to about their waist level. Allow your head to droop and keep your eyes closed; make sure you are completely relaxed and supported only by their grip (takes trust, I know). Stay this way quietly for perhaps a minute. Then have them slowly begin to lower your arms to the floor, and call out just before you think you're going to hit it.