My throat dry I don't know how far back down
Your statement is quite simple, and short. Maybe that's why I have questions.
Is the dryness just your throat? How far back, down?
If you tongue and mouth in general is dry and even painful it may be your are breathing through your mouth when asleep. Do you suffer from nasal congestion?
You may get some relief from use of a dry mouth preparation, over-the-counter stuff and I believe will say something about "dry mouth" not "dry throat".. but the preparation will surely coat the back of the mouth enough for you to notice the difference.