Sleeping and feeling dry mouth may be due to periodontal inflammation, salivary gland disease or dry syndrome, etc. The exact cause needs to be confirmed after checking in the hospital. 1. Periodontal inflammation: when the oral cavity caries, apical periodontitis, pulpitis or periodontitis local inflammation, due to the stimulation of inflammation may trigger the salivary glands insufficient secretion, which leads to sleep dry mouth. 2. Salivary gland diseases: When the salivary glands are inflamed in submandibular inflammation or Scheglund’s syndrome, atrophy or abnormal secretion of the salivary vesicles may lead to too little saliva. 3. Dry syndrome: Dry syndrome is an autoimmune disease involving the glands, with decreased secretion from the lacrimal and salivary glands, and the main symptoms are dry eyes and dry mouth. Sleeping feeling dry mouth can be first appropriate supplemental water to observe whether there is no improvement, if the symptoms persist for a long time, it is recommended to go to the hospital in time for examination and treatment.