If you're losing circulation (as in you're get pins and needles, and/or pain after the numbness) in any part of your lower leg - this is an indication of compartment syndrome.
If you're leg is going numb with no pins and needles/pain, i have the same issue. My doctor seems to think it's a nerve problem, and i'm giong to get it looked into. But if you're getting compartment syndrome that's a little bit more serious.