A sudden dry mouth in the middle of the night may be a lack of water. If it is in the dry weather of autumn and winter, or the bedroom has heating, open air conditioning, etc., resulting in low air humidity, and the person is in a sleep state, several hours can not drink water, coupled with the existence of open-mouth breathing when sleeping, it may lead to oral mucosa dehydration, the sudden appearance of dry mouth in the middle of the night, through timely replenishment of water, or improve the environmental humidity, dry mouth can be relieved. However, if you still do not see relief, you need to consider pathological factors related to diabetes, dry syndrome or nephropathy, etc. 1. diabetes: because the body is in a high blood sugar state, on the one hand, it will lead to an increase in plasma osmotic pressure, stimulating the water drinking center; on the other hand, there will also be osmotic diuresis, resulting in an increase in urine volume and water shortage in the body. Due to the reduction of water consumption at night, it will cause a sudden dry mouth in the middle of the night. In addition to this, it is accompanied by symptoms such as excessive drinking, polyuria, polyphagia and weight loss. If the above situation occurs, it is recommended to consult a doctor in time, and fasting blood glucose test, glucose tolerance test, glycosylated hemoglobin measurement, etc. can be used to help diagnosis. 2. Dry syndrome: It is a chronic inflammatory autoimmune disease that can lead to a decrease in salivary gland secretion. Because of the decrease in saliva and the inability to drink water in time, it can cause sudden dry mouth in the middle of the night, usually accompanied by dry eyes, rash and other symptoms. Such patients can go to the stomatology department, through saliva flow measurement, hematological examination, etc. to help clarify the diagnosis; 3, kidney disease: the main role of the kidneys is to regulate the body’s water, electrolytes and acid-base balance, excretion of metabolites, when the kidneys have lesions, such as uremia, pyelonephritis, hydronephrosis, etc., resulting in abnormal glomerular filtration, it may cause the body dehydration. During the daytime, it can be relieved by drinking water, but at night, when you cannot rehydrate in time, you may have a sudden dry mouth in the middle of the night. If it is also accompanied by facial swelling, edema of the extremities and pain in the lower back and abdomen, it is recommended to seek medical attention promptly to avoid delaying treatment. The presence of renal lesions can be clarified clinically through imaging examinations such as ultrasonography and x-ray examination.