I'm not sure it's allergic because this only happens as a reaction to my mite allergy, so basically during sleep, but when it comes to pollen, it's diverse. I tried nasal corticosteroids with antihistamines and mast cell inhibitors against it. I think only the corticosteroids help a little bit for a short time. The antihistamines and mast cell inhibitors have a longer half-time. This supports my assumption that it isn't allergic but inflammatory. But corticosteroids are also immunosuppressive, so they might give EBV and other pathogens an advantage.
If I have dry mucosa, NAC helps. My throat might still feel like sandpaper or like I have fake thirst, but it's not dry at least. Most CFS/ME patients are cysteine deficient anyways, I presume, due to the methylation blockage.