During the deepest stage of sleep, when dreaming is most likely to occur, part of the brain shuts down body movements so you won’t go hurling yourself around the bed as you dream of chasing tigers. If you awaken from this stage before your body does, you will actually be momentarily paralyzed; if your brain is still generating dream images, you will, for a few seconds, have a waking dream. That’s why those figures on the bed are dreamlike, nightmarish—you are dreaming, but with your eyes open.
