Why Do I Have Cramping In My Calves That Is Usually In The Left Leg While Sleeping Which Gets Painful?

Hi, I have cramping in my calves (usually left leg) while I sleep. It is very painful and wakes me up. My calf is actually hard. It’s not a vascular problem as I have had that checked. I’m a 63-year old woman in very good health. My sister told me she has these too.