What causes hands to go numb at night?

A couple of things: Wnat is your sleep position? Sleeping with the arms over the head, bent at the elbow or other positions can cause the hands to be numb or partially numb. You may have a neck problem and would depend on the positon of the neck and the type of pillow your have. I would see your pcp, neurologist or neurosurgeon or orthopedist and get checked out.

Carpal tunnel?: The hands can go numb for a variety of reasons. One reason might be carpal tunnel syndrome where there is pressure on he median nerve, a nerve in the middle of the wrist. Your evaluation will include looking for this as a possible reason. There are other things such as vascular compression, nerve compression from other nerves and this will be part of your evaluation.