I Have Had Three Episodes Where My Left Leg Starts

I have had three episodes where my left leg starts feeling as if its asleep, and then it extends at the knee straight out and my foot turns inward. I cannot move the leg or foot when this happens. It only lasts a few minutes, and then the leg just drops as if someone were holding it and suddenly let go. The leg will remain "asleep" for several hours afterward. Once, it occurred to my left arm simultaneously. Any ideas?