It's cramp. I get the same from time to time (with exactly the same trigger). It's horrible way to wake up.
My normal tactic is to rub my calf muscle hard with my knuckles whilst whimpering like a little girl.
RB wrote:It gets everyone eventually. Unless I get run over or something I'm certain I'll die of some kind of cancer. Maybe soon, maybe when I'm 107 but the chances are it will be some variety of cancer that does for me and most of us.