In response to the above.
If the bed is cold, if the bedroom is cold, and if one leg is not covered by the blankets, the lower leg muscles of that leg will go into a cramp, or morning Charley horse. Muscles tighten before going into a cramp. A cramp is a sudden and severe tightening of the muscles.
I often feel my lower leg muscles in one leg tighten up. If I am still sound asleep, I do not feel the tightening but I wake up with severe pain in the lower leg muscles and my toes will be pulled back rather painfully.
The remedy is to rush to the shower and place the lower leg under hot water. Let the hot water run over the tight leg muscles for 10 to 20 minutes until one feels that the muscles have loosened up.