If a patient has shoulder pain when lying down, it may be related to the following causes: 1. There may be trauma to the shoulder joint. If there is damage to the joint capsule or ligaments in front of the shoulder joint, these structures may be strained when the patient is lying down, causing pain. Minor fractures or dislocations around the shoulder joint may also cause this condition.2. There may be habitual dislocation of the shoulder joint. This condition is often caused by the patient’s initial dislocation of the shoulder joint without thorough treatment, resulting in secondary damage around the shoulder joint, compression damage of the bone or injury related to the joint capsule. 3. Cervical spondylosis may exist. There are many patients who have a pillow that is too high or have a bad sleeping posture, so when they sleep, it may lead to some nerve roots of the cervical spine being stimulated by pressure, which in turn causes pain around the shoulder joint.