I've had the same problem for the last 3 days and sleep by 30 min interval. Only last night i realized what was going on.
If you don't want to read my whole story about my different failed attempt to resolve this, just skip to the last paragraph.
In sum, i got Pneumonia and my nose is filled with mucus all the time. I go thru a whole box of tissue a day to blow it all out. 3 days ago, i couldn't sleep anymore since i was breathing thru my mouth (nose stuffed), as soon as i start breathing thru my mouth, I could feel the whole air track being very very dry, which awakens me since the throat / tongue sends a sharp pain when it "tries" to rehumidify (swallow motion, but no saliva). When i wake up, i drink some water (painful) but it rehydrathes my mouth / air track. Yet, the whole thing happens again as soon as I start breathing with my mouth again. The following is what i tried to resolve the problem:
Added humidifier to my room and blows over my face: didn't help at all
-Took Cepacol (lozenge that numbs the throat); Kinda of works for 30 min as it force production of saliva and i feel less my throat, but after 30 ish minutes its the same again. I cannot take ten of these per night... My tongue feels really irritated.
-Drink juice / 7up: helps a bit, as it seems to stay a little bit longer than water in my throat, probably messing up my teeths though...
-Breathing directly from the humidifier: It works! breathing very humid air keeps my air track humid. Tried for many hours... then Read on it and it would appear doing this is very dangerous, as water droplets enters your lungs, then this could cause serious infections. I really don't need another infection at the moment...
-Took some cough syrup: Kinda works, if you don't rince your mouth with water: basically there's a layer inside the air track that seems to stay and doesn't dry when you breath.
-I was thinking about gulping a spoon of Olive oil: Didn't try it. was just an idea.
After all that, i though if i could get my nose to clear, then all this could be prevented, I tried:
-Hydrasense (salty water spray in nose): really didn't do much
-Otrivin (decongestion spray): Works for some times, but as soon as the mucus builds up, its blocked again
-Steroid spray (prescribed by doctor when i explained my situation): its like a stronger version of Otrivin, but as soon as mucus builds up, specially when i lay down, its blocked again
-Breath Right Strips: Helps a bit as it makes the nose cavity bigger, but when too much mucus builds up, its blocked again.
-Secaris nose gel: I tried to clean my nose, then apply a layer of nose gel: Its keeps the nose moist, but does not help for the blockage
-Shower / Bowl of hot water + cloth to cover and breath: It does work, but as soon as i lay down, its starts to block
-Tilting my head back and try sleeping sitting in 45 degree angle: it works, the mucus seems to go the other way (down the throat) and its not blocked anymore. Hard to sleep though. Furthermore, i realized that my nose and the air track is very dry again... Hence, instead of mouth + air track dry, i get nose + air track dry... Meaning unblocking my nose does not solve the problem...
Finally on the forth day, i was so tired and lazy i just stop blowing my nose... and then it hit me: Its the fact that I've been blowing constantly my nose to get the all mucus out + tried to spit out all "slimy" saliva out of my mouth, and the constant drinking of water, caused my air track to be VERY SQUEAKY CLEAN. That was why the air track was getting dried up so fast. So people: Stop blowing constantly your nose / spit out all slimy saliva from mouth, and it wont dry out as fast anymore... Its a good thing to get a bit of mucus going down the throat...
I hope it will help someone, as forums / internet has always been a source of knowledge for me in time of illness.