The causes of chest pain caused by sleeping on the side include the following: First, consider that it is caused by the body’s respiratory system diseases, mostly due to the body’s acute and chronic bronchitis, ruptured pulmonary blisters, spontaneous pneumothorax, etc. When the body sleeps on its side, the pressure in the chest cavity is unevenly distributed, which causes chest pain, and will be accompanied by symptoms such as breathlessness and chest tightness. For this cause of chest pain, you need to go to a hospital for thoracic surgery and take a chest X-ray or chest CT examination to clarify. Secondly, it is considered to be caused by cardiovascular system diseases, including myocardial ischemia and exertional angina pectoris, because when sleeping on the side, the blood circulation of the heart changes, causing insufficient blood supply to the heart muscle and chest pain, which requires an electrocardiogram or dynamic electrocardiogram for clarification. Thirdly, it is considered to be caused by intercostal nerve including intercostal muscle pain, mostly manifested as pain at night when resting, which can be relieved by resting or with the application of blood-stasis activating drugs.