It is possible that what you experience is completely normal. Just before falling asleep, the muscles relax so much that the receptors in the muscles do not get enough information about the position of the body. That is why the brain receives information that the pressure in every muscle is the same which it interprets as flowing or floating, two conditions in which there is no additional contact pressure on the muscles.


Various people experience twitching of the muscles with unexpected involuntary movement of a limb. This is because the voluntary control of the muscles by the brain is decreased, and the muscles are controlled only by the spinal reflexes. If the muscles relax before the person completely falls asleep, it might be recognized as shaking and might even interrupt the falling asleep cycle.