The falling asleep effect is really your nerve being deprived of oxygen (anoxic) causing conduction problems-- usually from laying on it adding extra pressure . Good news it resolves pretty quickly-- no permanent damage... The pain is there to help arouse you so you are aware of the problem and you fix it without permanent damage. Your nerves are more to blame. Nerves are like tiny threads that run through your whole body, and they carry messages back and forth between your brain and body. When you sit on your foot you temporarily compress the nerves in that area. These nerves can't send messages back to the brain normally, and so for the moment, the connection is cut off and you don't feel anything. After you stand up the nerves are no longer compressed, the feeling in your foot soon comes back. It might feel a bit tingly as this happens, like pins and needles or even a bit painful. But it only lasts a few seconds as the connection returns to normal, and it won't hurt your body.