Numbness in the arms while sleeping is usually seen in the following two conditions: 1) numbness caused by neuropathy; 2) numbness caused by vascular disease. Numbness due to neuropathy is most commonly caused by cervical spondylosis or herniated cervical discs that compress nerves, resulting in radiating pain or numbness in one or both upper extremities. Generally, when the nerve is just compressed in the early stage of cervical spondylosis, it is painful, and after a longer period of compression, numbness and decreased skin sensation in the painful area may appear, mainly due to pathological changes of nerve ischemia and necrosis, and then numbness may occur. If the numbness is caused by the second condition, that is, vascular lesions, most of them are due to poor circulation in the arteries and veins of the upper extremities and lack of blood flow to the local muscles, which leads to numbness. Generally, numbness can be reduced after activity of vascular lesions, but in the case of neuropathic numbness, there may be no change in numbness after activity.