I wake up to a dislocated jaw like every night--why?

Sleep behavior: It could be the way you sleep. You may have symptoms of TMJ syndrome. See your dentist or oral surgeon.

Clenching in sleep: Very likely you clench or grind during sleep and cause the fatige or malpostion of your muscle or ligament around the joints. You should see your dentist for evaluation and a night guard might help.

Depends: Depends on what you mean. True jaw dislocation is your jaw locked wide open. You may be referring to the disk malposition causing your jaw to get stuck closed or just partially open. Different problems with different solutions. See oral surgeon for advice.