As soon as you sleep, dry mouth and bitter mouth can be caused by a variety of reasons, the following are common: 1, diabetes: diabetic patients because of elevated sugar in the blood, resulting in increased osmotic pressure, stimulating the thirst center to produce dry mouth, bitter mouth and other symptoms; 2, hyperthyroidism: can be found by checking the three thyroid function in the blood, such patients often have a more irritable mood, panic, sweating, hand shaking 3. Urogenital disorders: Although urogenital disorders are rare in clinical practice, they are not uncommon because of the lack of AVP (arginine pressor) in the patient’s body, the patient keeps urinating, resulting in dry mouth and bitter mouth symptoms, which are more obvious at night when sleeping; 4. This can also lead to dry mouth and bitterness; people who are used to open-mouth breathing are also prone to dry mouth.