A dry or stuffy bedroom can also cause dry mouth. Some people find that humidifiers are useful in adding moisture to the bedroom air during sleep. In addition, you might try drinking a glass of water before going to bed to reduce the chance of dry mouth.
Unusual mouth dryness may be a side effect of medical conditions such as diabetes or medications such as antihistamines. Talk to your doctor if dry mouth is a persistent problem. Your doctor may also prescribe a medication to help increase your saliva production.