Waking up from sleep with a bitter mouth may be caused by stomatitis, gastritis, cholecystitis, diabetes or bad oral habits, psychological factors and so on. 1. Plaque irritation in the mouth caused by gingivitis, periodontitis, lingual inflammation and other diseases may cause waking up with a bitter mouth. 2. Chronic gastritis patients with insufficient gastric power or Helicobacter pylori infection will have a bitter mouth performance. 3. Those with cholecystitis may have bile discharge and bile reflux. 4. Diabetic patients with poor blood sugar control will have a bitter mouth. 5. Bad habits such as frequent smoking or drinking too much alcohol can lead to a bitter mouth. 6. Psychological factors and other reasons can also have an abnormal sense of taste and a bitter mouth.