Chest pain when sleeping on the side may be caused by abnormal sleeping posture, chest trauma, costochondritis and so on. 1. Abnormal sleeping posture: If you keep sleeping on your side for a long time, it may cause pressure on the soft tissues of one side of the chest, resulting in poor blood circulation and chest pain. 2. Chest trauma: If the chest area is injured by direct or indirect violence, it may cause soft tissue injury or bone fracture in the chest area, and sleeping on the side will aggravate the fracture situation, resulting in severe pain in the chest. 3. Costal chondritis: when the patient suffers from costal chondritis, sleeping on the side may aggravate the stimulation of soft tissues, and chest pain occurs. In addition, the possibility of cardiovascular system diseases and pleural diseases cannot be ruled out. It is recommended that when patients have chest pain when sleeping on their side, they should go to the hospital in time, and actively treat the cause of the disease.