When you wake up with a bitter mouth after sleeping, you need to consider whether there is a bile reflux-related reason, because after sleeping, the whole body is in a flat state, and due to the gravity factor, bile can easily appear to reflux and thus reach the stomach, esophagus and mouth to appear the symptoms of bitter mouth. In addition, the vagus nerve excitation after sleep at night will promote the secretion of bile, which is more conducive to the reflux of symptoms of bitter mouth. Finally, if there are related biliary tract diseases and pyloric valve relaxation, bile reflux is more likely to occur, which can lead to the symptoms of bitterness in the mouth.