Can post nasal drip cause dry mouth? I wake up with dry mouth then goes away after drink water. I always swallowing thin mucus that won't come up. Can t

Mouth-breathing? You likely have nasal obstruction as well and mouth-breathing while asleep can give you dry mouth. Consult your doctor to see if you have nasal problem and then observe whether reducing the nasal obstruction leads to improvement in your dry mouth. Dry mouth may also be caused by inflamed salivary glands presumably from an autoimmune process.