What causes night cramps?!

For most cramps, stretch. If a spasm strikes the calf (by far the most common cramp site), pull the front of the foot up toward the knee. Since cramps usually result from muscle fatigue, you may be able to prevent such spasms by gently stretching before you exercise your calves. Stand a few feet from a wall, brace yourself against the wall with your hands, and lean forward, keeping your heels on the ground until you feel a pull in your calves. This maneuver before bedtime can also help prevent unexplained nighttime spasms.
If the cause isn't muscle fatigue, your physician may find other, possibly treatable causes. These can include circulatory problems, hyperventilation, an underactive thyroid, and low blood levels of calcium or (rarely) magnesium, potassium deficiency.
I hope this helps you. And good luck.

I had this when I was pregnant and was advised to eat a banana every day, apparently it's due to low magnesium/potassium and bananas contain both of these. It did work!

My GP