Sudden acid reflux may be caused by improper diet, gastroesophageal reflux, gastritis and other reasons. 1. Improper diet: Eating too much stimulating food, being too full or too hungry may lead to increased secretion of stomach acid, and acid reflux will easily occur when stomach acid secretion increases. 2. Gastroesophageal reflux (GERD): In this type of patients, the food and acid in the stomach tend to back up into the esophagus, which may lead to the sudden appearance of acid in the mouth due to the reflux of stomach acid. The most typical symptoms of GERD are acid reflux, heartburn and reflux. 3. Gastritis: Patients suffering from gastritis generally have relatively high secretion of gastric acid, and patients are prone to symptoms of acid reflux. Acid reflux is a phenomenon caused by excessive secretion of gastric acid. If the phenomenon of acid reflux occurs for a long period of time, it is recommended that the patient go to the hospital in time.