Chest pain once lying down may be caused by reflux esophagitis, chest tissue injury, angina and other factors. 1. Reflux esophagitis: with the change of body position, the patient may have inflammation of the esophagus caused by reflux when he/she lies down or lowers his/her head, and reflux esophagitis may cause chest pain. 2. Chest tissue injury: when the patient has chest wall or ribs, rib cartilage or chest soft tissue injury, chest pain may be induced when the patient lies down or changes the movement position. 3. Angina pectoris: when lying down, it may lead to an increase in the volume of return blood, which may increase the load on the heart and sometimes induce angina pectoris. If there is a problem of chest pain when lying down, it must be taken seriously, and it is recommended to go to the hospital for relevant examinations, to clarify the cause of the disease, and then standardized treatment.