Dry mouth and bitterness in bed may be caused by mental factors, oral diseases, gallbladder diseases, stomach diseases and so on. 1. Mental factors: study, life and work stress, lack of sleep may cause autonomic nervous system disorders leading to sleep up dry mouth, bitter mouth. 2. Oral disease: do not pay attention to oral hygiene, no brushing at night, food residues in the teeth gap fermentation leads to dental caries, periodontal inflammation, mouth ulcers, etc. will cause dry mouth and bitter mouth. 3. Gallbladder diseases: such as gallbladder stones, acute cholecystitis, etc., leading to bile discharge is not smooth, sleep up a dry mouth and bitter. 4. Gastric diseases: such as bile reflux gastritis can cause bile to reflux to the upper gastrointestinal tract, causing dry mouth, bitter mouth. Sleeping up dry mouth and bitter mouth may also be other reasons, it is recommended to consult a doctor in a timely manner to identify the cause of the disease and comply with the doctor’s instructions, in order to avoid delaying the condition.