The past 2 nights I woke up with a "charlie horse" type of cramp in my neck, what could be causing it?

The only time i have ever experienced charlie horse is when i was pregnant, i would get them in my legs at night. i took my prenatal vitamins, so i do not tink it was a magnesium or potium deficiency. what else could cause this now to happen in my neck? what do i do to prevent it?