Tingling in the left hand after waking up may be improper sleeping posture, cervical spondylosis, rheumatoid arthritis, cerebral ischemia and so on. 1. Improper sleeping posture: mainly refers to the left hand when sleeping pressure to the left hand, the left hand blood circulation, nerve conduction caused by obstruction of numbness. 2. Cervical spondylosis: caused by long-term strain injury, cervical degenerative disease, etc., when the attack compresses the nerve root of the left upper limb, the left hand numbness, neck stiffness, etc. 3. Rheumatoid arthritis: an autoimmune disease caused by heredity, infection, abnormal immune function, etc. It stimulates the peripheral nerves of the left hand during the onset of the disease, manifesting as numbness, swelling and pain in the left hand. 4. Cerebral ischemia: mostly occurs in middle-aged and old people, caused by arteriosclerosis, hypertension, poor vascular conditions, etc. Typical symptoms are numbness in the left hand accompanied by dizziness, difficulty in activities, etc. There are many other causes of numbness in the left hand while sleeping, if the symptoms persist or aggravate, it is recommended to go to the hospital as soon as possible, with the help of the doctor to identify the cause and take targeted treatment.