There are many reasons for side sleeping chest pain, such as physiological phenomenon, costochondritis, pleurisy, myocardial ischemia and so on. 1. Physiological phenomenon: keeping sleeping on the side for a long time can cause the side tissues to be compressed for a long time, which affects the local blood circulation, and thus chest pain will appear, which will be gradually relieved after changing the body position. 2. Costal chondritis: costal chondritis is an inflammatory reaction of the cartilage at the junction of the ribs and sternum, which may be caused by severe coughing, chest trauma, chronic strain, and may show chest pain when sleeping on the side, which will be relieved after lying down. 3. Pleurisy: pleurisy is an inflammatory reaction in the pleural cavity, which can show chest pain and chest tightness, and the symptoms are more obvious when sleeping on the side. 4. Myocardial ischemia: coronary atherosclerosis can cause insufficient oxygen supply to the myocardium, myocardial ischemia, unable to meet the demand of the myocardium for oxygen, so it will show chest pain, especially when sleeping on the side of the symptoms are more serious. Side sleep chest pain has many reasons, if the phenomenon of long-term and can not be relieved, it is recommended that patients go to the hospital as soon as possible, in accordance with the doctor’s instructions to take standardized treatment.