I've had it for years (and years). I really feel (my own situation will attest to this) that it's a reaction by the nervous system to anxiety or flat out fear. I get waves of it, particularly released from my feet that even I am allergic to. Every minute of my life now is consumed with this crap. Debilitating? That would only begin to describe it. I do know that, in my case, smokes, caffeine, any stimulants make it much worse. If I have a hangover, and I've had coffee and a few smokes. I could walk in to a gym and some would start sneezing. My Dr. doesn't know what I'm talking about.
Yes it is called brain fog, your ability to think is gone
I have the same problem as well. If you look up Candida it's one of the side effects, as well as fatigue. I notice when I am on the Candida diet that those side effects improve, but I have never disciplined myself to stick to the diet and see it through to the end.