For arm pain while sleeping, it may be caused by frozen shoulder and rotator cuff injury, as follows: First, frozen shoulder: it may be frozen shoulder, frozen shoulder will appear pain around the shoulder joint, including the outer side of the upper arm, armpit, shoulder joint before and after the shoulder blade area, neck and shoulder pain, the pain range of frozen shoulder is relatively wide, and the pain will be aggravated at night. Second, rotator cuff injury: rotator cuff injury is considered, rotator cuff injury often appears among middle-aged and old-aged patients, due to the degeneration of rotator cuff and tendon, brittleness increases, and localized pain and lifting weakness often appear, and there will be pain in the shoulder joint, acromion and the anterior and posterior aspect of the shoulder joint at night, and the pain will be more obvious at night.