What causes hand numbness while asleep?

Nerve compression. Numbness can occur from various reasons. Some potential causes include vitamin deficiency, nerve damage, nerve compression, alcohol over consumption, side effects of different medications, or as a result of different systemic medical conditions such as diabetes. Get evaluated by a professional to determine the diagnosis. Treatment is based on the diagnosis.
Numbness in hand. Numbness in the hand while asleep usually arises from compression of the blood supply to that area from lying on the hand. This should go away quickly once no longer lying on the hand. Chronic numbness in the hand that does not go away could be related to nerve entrapment. Numbness can also be a sign of underlying disease so this should be discussed with your doctor if lasting more than minutes.