The left side of the stomach lying down pain may be indigestion, gastric ulcer, stomach tumors and other causes, the main general treatment, drug treatment, surgical treatment and so on. 1. Indigestion: most of them are caused by improper diet, such as eating too much greasy food or overeating, which will lead to food retention and cause pain, you can get out of bed properly, and abdominal massage can promote intestinal peristalsis, relieve the symptoms, and take drugs to promote digestion, such as moxapride and domperidone. 2. Gastric ulcer: often because of ulcer damage to the gastric mucosa, when lying down, the gastric acid may cause stimulation of the gastric mucosa as well as gastric extrusion, thus causing pain, generally need to take acid-suppressing drugs, such as omeprazole, rabeprazole, and and mucosal repair drugs such as bismuth potassium citrate, aluminum sulfate, and so on. 3. Stomach tumors: including benign and malignant tumors, when lying down due to the tumor caused by extrusion, causing pain, need to take timely surgical resection, if the tumor is malignant, after surgery with further radiotherapy. All the above medicines should be used under the guidance of doctors, and patients should not use the medicines by themselves arbitrarily.