If you have a dry mouth at night, here are 8 possible reasons.

1. Digestive Problems.
The most common digestive problems and how to prevent them – LivGastro.
What you eat before bed can affect the functioning of your digestive system. Fatty, spicy, or salty foods are especially discouraged as a nighttime snack, as they can irritate the stomach and make digestion difficult while you sleep.
These foods also absorb water from the body and can increase fat levels or blood pressure, worsening the problem. Since the body continues to digest while you sleep, it may draw fluids from other areas, leading to a dry mouth upon waking.
2. Liver Problems.
The liver plays a vital role in eliminating toxins from the body. When it is overloaded or not functioning properly, toxins can accumulate. A subtle symptom is repeatedly waking up with a dry mouth. If this occurs frequently and there is no apparent cause, it is advisable to consult a doctor.
3. Dehydration