Another and common cause of that could be compression of the nerves as they run through the elbow if you sleep in a partial fetal position with your arms bent. If the numbness and tingling resolves in a few seconds when you straighten the elbow, that would comfirm that. Also, if the numbness and tingling is confined to the pinkie finger and the outside of the ring finger, that is a definnite sign of compression of the ulnar nerve, which is commonly compressed at the elbow. (symptoms in the rest of the hand point to the median nerve and could more likely be carpal tunnel or a compression in the elbow.) If it is a nerve compression, just wrap a towel around trhe elbow before bed to keep it straight. After a few weeks the irritation of the nerve should heal.