<s>[INST] I have an extremely dry mouth and throat at night.  I can't produce spit and so I have to get up and gargle w/water or a solution made for dry mouth.  I believe that this started before my knee surgery about a year ago and I was put on Hydrochlorothiazide 25mg.  Is there any medical issues that would cause my mouth to be this dry.  I do not have a problem except when I sleep. [/INST] Hi..Thanks for the query.Dry mouth and throat at night only and not during the day is commonly seen due to mouth breathing habit..Some individuals have a habit of breathing through mouth while sleeping or sleeping with open mouth causing the mucosa of mouth and throat to dry..So first of all you need to sleep with closed mouth and enforce nasal breathing..For this you can stick a vertical strip of micropore tape/doctor's tape over your closed lip just before sleeping..This will enforce nasal breathing and will reduce drying of mouth..You should also use a humidifier in your room..If the symptoms does not get better then you can consult an Oral Physician and get checked for any medical condition..For now it does not look like any medical problem..Hope this helps.Regards. </s>