What caused my leg (calf muscle) to cramp up and have severe pain?

Charlie Horse is the leg muscles responding to not enough calcium. If the bones aren't getting enough, they will take it from the muscles in order to fulfill their needs. Calcium is also necessary for healthy heart contraction. Might want to knock off the phosphates (sodas) which also deprives your bones from much needed calcium. Calcium/magnesium (nature's muscle relaxant) is a great daily nutritional supplement, and with the added Vit D, the calcium will be better absorbed. Do drink lots of milk as well.