I had a suspicion, and it is now verified. Mom came up to look at my place, and she found places on various walls where there are mildew spots. I discussed my theory that cat allergies are only a minor problem for me, and she actually agreed that there are a number of factors. I think mold and mildew are very significant ones. These are allergens that I have always reacted extremely strongly to, and no matter how much cleaning I do with the cats the symptoms only dissipate for a few moments. So even when my air is free enough of animal dander that I should be breathing well, I am still breathing like I am allergen-toxic--and I probably am.
This problem is not likely to go away for quite a while... We have a leak in the roof that needs to be fixed and other stuff that needs to be done. Mom wants to paint up here, and I'm dreading that because of the fumes... I could go and stay downstairs, but I can't really take my cats down there and I don't want to leave them up here alone. But most of all, I just want to be able to breathe. I'm tired and I can't stay on CPAP all the time.