Numbness of the hands once sleeping may be caused by incorrect sleeping posture, low temperature and carpal tunnel syndrome. 1. Incorrect sleeping position: Sleeping on the side can lead to compression of the hands with poor blood circulation, which can cause hand numbness, accompanied by the symptom of cold hands. Taking massage, hot compresses and changing the sleeping position will eliminate this symptom. 2. Low temperature: when the indoor temperature is too low, sleeping with your hands outside leads to cold hands, there will be symptoms of numbness in the hands while sleeping. Doing local massage or soaking hands in hot water can relieve the symptoms. 3. Carpal Tunnel Syndrome: Carpal Tunnel Syndrome is a relatively common cause of hand numbness during sleep, mainly due to patients engaged in long-term repetitive labor work caused by, such as frequent hand rubbing clothes, long time driving, etc.. It is easy to have wrist posture problems during sleep, which induces the symptoms to appear. There are many other reasons for the numbness of the hand when sleeping, the specific condition should go to the hospital for examination, clear causes under the guidance of the doctor for targeted treatment.