Suggest Exercise To Reduce Cramping In Feet At Night

for the past few weeks I have been getting severe night cramps in both my feet. akes me up at night. On seeing a physio she gave me exercises raising my leg one at a time bending it and moving the foot up and down - tried this but straight away cramp in my foot happened. when I wake in the morning, my foot cramps are so bad I cannot stand on my feet for a while. However I don t seem to have aproblem during the day. Any clues as to wht exercise I can do to relieve these cramps. I do take crestor - 5.2 Can you help ? Jenny Upton