there is quite a few possabilities for what is causing this. one of the more common is lack of circulation. especially in the colder months. if our body has trouble with circulation due to the swelling of muscles. it is easy for the blood flow to be restricted. this restricted blood flow creates the feeling of tingling and numbness. it is our feet falling asleep. many of us find it useful to wear woollen socks to help insulate against cold. and to do basic stretching exercises to keep the blood flowing. it have one of the "tens" machines, I use it to help stimulate my muscles and increase blood flow. it is something I recommend talking to a doctor about, on your next visit.