Did you sleep on that side? If you did, it could be that you have compressed the sciatic nerve that has made it numb and that this will resolve in time. Do you get pain as well as numbness going further down the leg? If so, it is possible that you could have sciatica. Sometimes you can have sciatica with numbness and no pain. Anyway, go and get this checked out and if this is sciatica, then I would suggest that you go and have some acupuncture treatment. Acupuncture is great for sciatica.