Stomach upset after staying up late may be caused by improper diet, nerve irritation, stomach diseases and other reasons. 1. Improper diet: stomach upset is usually caused by excessive secretion of gastric acid, which stimulates the gastrointestinal mucosa, if the patient eats too much food at night, it will cause excessive secretion of gastric acid in the evening, which is easy to cause the symptoms of stomach upset after the patient stays up late. 2. Nerve stimulation: when the patient stays up late, it is easy to lead to autonomic nerve disorders, which will stimulate increased secretion of gastric acid, gastric acid stimulation of gastrointestinal mucosa, so that the patient produces symptoms of discomfort. 3. Stomach diseases: when the patient himself has gastric ulcer, duodenal ulcer and other diseases, gastric mucosa is damaged, gastric acid stimulation of gastrointestinal mucosa discomfort symptoms. When staying up late, patients are generally fasting state, which can easily lead to stomach discomfort, acid reflux stomach pain and other symptoms. If the patient exists after staying up late stomach upset symptoms, it is best to go to the hospital for examination, follow the doctor’s advice for treatment, in order to ensure good health.