Brain fog is comparable to dementia. It's common to hear it called brainflamation in the chronic illness community. Mine is so bad lately I can't even remember my symptoms to be able to talk to a Dr about how bad it is, let alone what I did 5 mins ago.
Prednisone the wonder drug. Can be a double edge sword the more you take it. Have you taken it long? It works by suppressing the immune system. The immune system causes inflammation which results in symptoms. The digestive system sends histamine and cortisone to the brain kicking off the inflammatory response.
Prednisone can increase risk of infection and weaken bones if they didn't tell you.
I was on it regularly until I started getting bronchitis on it. I really struggle with steroids these days, even for my asthma.
I go from not being able to sleep to being so tired I can't keep my eyes open. Only in extreme cases should you be on it all the time, like after chemo they do this sometimes.
So many food, lifestyle and environmental triggers. It's really not much different than an allergic reaction, just a wide range of symptoms.
Have you tried any of the antinflamatory diets and protocols yet? Elimination diet worked the best for me along with moving to a very dry climate. Less water means less biodiversity causing triggers. Less low barometric pressure too. Elimination diet is used to identify food triggers when an allergy test comes back inconclusive.

I have an autoimmune disease too so in my case there's visible inflammatory responses.
It's still debatable if fibromyalgia is inflammatory or not, more recent studies suggest it is, but a lot of the current medical providers will say it isn't.
My last PCP explained how there aren't enough tests available to be able to identify everything that could signal inflammation anyways. What we have now is what is most common amd easy to test for, if that makes sense. A lot of the treatments are the same like use of steroids, diet and exercise.

Wow! Thank you. You seem so well informed. As for predesone, I only take it during server times. I'll get like the 21 pill count down. I asked if I could take it all the time but was told that it had side effects, etc. Also I was once Fibro doesn't cause inflammation, do you believe that's true? I'd so, I surely have other issues that cause it. But thanks for explaining inflammation of the brain, I couldn't imagine what happened to me and was honestly a little scared. Should have know to come to the Fibro warriors site!😁 I'm not sure if you're on my team or I'm on yours but would love to keep in touch. Lmk I'm still not proficient at this but never give up! Thanks again. Zina💜👍🏻