Is it possible to drool while your sleeping and not even know it.?

I never see any wetness when I wake up, but I have been getting a sore on th corner of my lipped called angular cheilits and its caused by drooling (and a couple other things that I know I dont have) Plus I know I do sleep with my mouth open because my nose has been congested ever since I been pregnant, and I can only breath through my mouth. The doctors say its from drooling, but I never ever see any drool anywhere when I wake up. Please let me know if you have any advice or comments if this is whats actually happening. Thanks