What Causes Muscle Cramp In The Inner Thigh And Leg?

Hi, I would like to find out if there is anything I can do about stopping, preventing a muscle cramp in the inner thigh on my right leg ( right at the fat part of whree your knee is on the inside.) What happens is, occasionally I get this cramp seems to come on without any exercition and then causes so much pain, I have a vaso vagul attack. I am trying to learn as much as I can about what to do to prevent this.