The left arm does not hurt during the daytime pain at night, considering the physiological factors such as exertion, cold and other physiological factors, may also be frozen shoulder, humeral epicondylitis and other pathologic factors caused by. 1. Physiological factors: due to physical labor during the day, or cold at night and other factors, can cause muscle spasm and strain of the upper limbs, the body produces a large amount of lactic acid, lactic acid buildup, the symptoms of arm pain can occur at night when resting. 2. Frozen shoulder: Frozen shoulder is a sterile inflammation around the shoulder joint, related to trauma and strain, and adhesion of soft tissues of the shoulder joint can occur. The pain can be alleviated after daytime activities, and the pain of frozen shoulder can be aggravated at night due to the inactivity and low temperature when resting. 3. Epicondylitis of the humerus: Epicondylitis of the humerus, also called tennis elbow, is a sterile inflammation caused by trauma and strain, which can cause pain on the outer side of the elbow joint, especially at night when the temperature is low, and the pain may be more serious. The left arm does not hurt during the day, but at night there may be other reasons for the pain, it is recommended that the patient go to the hospital in a timely manner, for the cause of targeted treatment, usually take more rest, pay attention to local warmth.