Mouth breather here, always waking up with desert dry mouth. I've been mouth taping for a couple years now, including a couple of hay fever seasons. Love it. Even with my allergies, somehow your body knows to keep one nostril open, or knows to breathe out of a corner of your mouth.  https://www.mrjamesnestor.com/

I think they are a virus that flares when immunity is weakened. Good, real, sleep, and healthy gut, are underrated keys to strong immunity. I've never done it, but maybe try a sleep tracker app?