I suspect in my case the main brain inflammation comes from have a virus in my brain (my ME/CFS started with viral encephalitis), but I think gut inflammation pushes that brain inflammation to higher levels.
With severe GAD, I was a complete desperado, and was trying anything to reduce it. I'd try out any angle, or any idea, in the hope that something would work.
I used to find that snorting warm steam from a boiling kettle would help reduce anxiety. Obviously your nose has to be about a foot or so above the kettle, to give the steam a chance to cool a bit, as you don't want to burn yourself.
The warm steam I found would reduce inflammation in my nasal cavity and sinuses, and again this I believe reduces brain inflammation (I suspect that nerves in the nasal and sinus cavities signal to the brain, much like the vagus signaling, and this signaling will increase neuroinflammation).
Once your anxiety gets to what is medically classified as severe, you actually spend your entire day trying to reduce it. No other thought enters your head other than trying to reduce the anxiety levels. I spent around 7 years like that, so as you can imagine, I tried a lot of things! I guess you may be in a similar state with trying to deal with constant pain.