I have Sjorgens, and have the extremely dry mouth at night too. My dentist recommended OraCoat XyliMelts. They actually worked well once I could get them stuck to my gums. I also just started using Now toothpaste with xylitol in it, and that also helped for a couple of hours. My only other problem is that xylitol bothers my stomach, but I don't think that's a problem with most people.
Hope you can find some relief very soon.