Do you have a large neck measurement? Cos if you do, regardless of the amount of alcohol you have, or whether you have a cold, you are likely to sleep with your mouth wide open and snore. In which case it gets dry. It's even worse with alcohol. I'm not sure if I'm right about this bit, but if you are scraping your tongue that much are you not taking any natural moisture out of it, and making it dry?
Have a glass of water handy by the bed.
Here's to no more dry tongues