I suffer from this too,and it is soo painful.I actually can't yawn and stretch anymore,cos my legs would go into cramp.I agree with what everyone else has said,and I would add,that with me,drinking loads of water to prevent dehydration(especially in the hot,humid weather),certainly seems to help.Also.make sure you are getting your daily salt requirement.,cos,a lack of salt can lead to dehydration. I read that putting corks under your mattress can help.I tried it,and for a while,it did work.!..Good luck!