When you sit on your foot, you temporarily compress, or squash, 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. It's kind of like a phone call where your friend hangs up and you haven't yet: Your brain is saying "hello," but your foot isn't able to answer.So yeah, communication is just lost. If you don't like your feet to fall asleep then just switch positions, extend your legs or stand up and don't sit for long periods of times.
After you stand up or uncross your legs and 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.
Hope you found this interesting and a great topic for the dinner table and tell some great stories about when your foot, hand, leg has fallen asleep.