Waking up with stomach pain and sitting up comfortably may be caused by physiological reasons such as overeating and pathological reasons such as reflux esophagitis. 1. Physiological reasons: overeating leads to a large secretion of gastric acid, and when you fall asleep, your body is in a horizontal position, so gastric acid can easily stimulate the cardia and cause stomach pain. When you sit up, your body is in an upright position and the stomach acid does not easily stimulate the cardia, so it is more comfortable to sit up when you wake up with stomach pain. 2. Reflux esophagitis: The relaxation of the esophageal sphincter leads to the reflux of stomach contents into the esophagus when you fall asleep, which leads to inflammation and stomach pain. When you sit up, due to gravity, the stomach contents are not easy to reflux, so you will feel more comfortable. There may be other reasons for waking up with stomach pain, so it is recommended that you go to the hospital in time to get a clear picture of the cause of the problem under the guidance of your doctor, and then give targeted treatment or therapy.