Sleeping on the side of the pressure shoulder pain may be localized compression, frozen shoulder, cervical spondylosis, and so on. 1. Localized compression: sleeping on the side, one shoulder is pressurized for a long time, and the blood circulation is not smooth, which can trigger numbness and pain in and around the shoulder. 2. Frozen shoulder: Shoulder joint soft tissue degeneration or long-term excessive activities, triggering the shoulder joint capsule and its surrounding ligaments, tendons and other injuries, the occurrence of chronic inflammatory diseases, which can be manifested as shoulder pain, shoulder joint activities are limited. 3. Cervical spondylosis: Neurogenic cervical spondylosis can cause shoulder pain because the diseased tissues of the cervical spine form pressure on the nerve root, causing radiating pain in the shoulder. Sleeping on the side of the pressure shoulder pain may also have other reasons, it is recommended to go to the hospital in a timely manner, improve the examination to clarify the cause of the disease, and then give targeted treatment or treatment.