Lateral chest pain is considered to be related to traumatic diseases, gastroesophageal reflux disease, pulmonary diseases and other causes. 1. Traumatic diseases: for example, strenuous activities, heavy physical labor, etc. can make violent external force on the chest local soft tissue caused by injury or rib bone, fracture and so on. When sleeping on the side, the injured part is squeezed, thus chest pain occurs. 2. Gastroesophageal Reflux Disease (GERD): GERD, especially when sleeping flat on the back or in the side position, because of the reflux of gastric contents and gastric acid stimulates the esophageal mucosa, which leads to the occurrence of chest pain symptoms. At this time, it is recommended to go to the hospital for gastroscopy, which can clarify the disease. 3. Lung diseases: for example, pneumonia, pleurisy, pleural effusion, etc., can lead to inflammatory exudation, stimulate the wall pleura and cause chest pain symptoms, pain can change with the change of body position, so the chest pain will be aggravated when lying on the side. Side lying chest pain, should be timely to the hospital to seek medical treatment, clear causes, early detection, early treatment, conducive to recovery.