text: what is the cause? sometimes in the night i wake up and my tongue feels like sandpaper and is very dry what is the cause? well, for starters, maybe cut back on the coffee a little.  caffeinated beverages are dehydrating.  actually, though, i think it's probably as simple as breathing through your mouth while you're sleeping.  is it possible you have a sinus infection or a deviated septum?    you might want to give those nighttime nasal strips a shot.  if you're breathing through your mouth while you sleep because your nasal passages are stuffed up, it could help.