The neurological disorder that causes dry mouth is Sjogren's syndrome which is an autoimmune disease which damages the glands which produce saliva and tears.
Sjogren's syndrome causes your body's immune system to attack the glands that are responsible for producing moisture which includes those in the mouth and eyes and can lead to and cause dry mouth and dry eyes.
Although Sjogren's syndrome is mainly known for it's effects on moisture producing glands and it can also have neurological complications like peripheral neuropathy or numbness or tingling in the feet and hands.
Dry mouth can also be caused by dehydration, certain medications, diabetes, nerve damage in the head and neck area and much more.
If you have persistent dry mouth and it's not relieved by drinking water and staying hydrated then you should see a doctor to rule out any other underlying health issues.
Dry mouth can also be caused by stroke, yeast infection in the mouth, diabetes, HIV/AIDS or even Alzheimer's disease.
Snoring and mouth breathing with your mouth open can also cause dry mouth.
Most people that have Sjogren's syndrome live long lives with a life expectancy comparable to the general population although some people may experience reduced lifespans due to complications such as interstital lung disease or even lymphoma.
While Sjogren's syndrome is a chronic autoimmune disease it does not always shorten life expectancy for most people that have it.
Sjogren's syndrome primarily affects your moisture producing glands in your mouth and eyes, although it can also impact other organs which include the lungs, joints, kidneys, blood vessels, digestive organs and nervous system.