Hi Doug,
So sorry to hear about what you are going through. It's so hard not to be able to think clearly or feel stable in space - feeling strong in body and mind are the basics of wellbeing. Having experienced both of these symptoms along the way myself, I can commiserate.
The brain fog issue is quite complex...there can be so many contributors. I've suffered with this for the duration of my TMJ and it's really scary to feel out of it for long periods. One thing I've found is that powerful muscle relaxants like flexeril have really exacerbated my brain fog. They have also made me feel dizzy, sort of off balance for much of the day after I've taken them. (Dizziness is an official side effect of flexeril actually). Powerful pain killers like percocet also make me foggy. If you don't really need them, I would eliminate them.
I think brain fog can also result from the body experiencing too much input of aggravating stimuli. When there's too much pain, tension or any other symptoms, I think fatigue and brain fog are the body's way of protecting itself by shutting down, essentially saying "I'm already dealing with enough and can't take any more in!". I notice that with my tinnitus, hyperacusis and other symptoms (including pain or not), my brain is already receiving so many messages, it's really hard to focus on any others. Kind of like being at a crowded, loud rock concert and trying to solve a calculus problem in your head...
Getting good sleep is so important in dealing with such physical issues and there are many ways to improve sleep without muscle relaxants. If you can, I would try getting off the drugs that exacerbate these symptoms for a period so that you can see exactly how much is being caused by the drugs and how much is caused by your condition.
In my experience, if you don't see a physio or other practitioner who specializes in TMJ issues, you may not be helped. I tried physio, acupuncture and chiro practitioners who did not specialize in TMJ and got no help whatsoever from any of these treatments. Once I found practitioners who were really informed about TMJ and up to date on how they could help treat it specifically, all three of these things helped me greatly.
I would recommend finding some second opinions, maybe a highly reputed NM dentist, and a chiro who specializes in TMJ- I believe that there are certain back/neck issues that can cause dizziness. My TMJ chiro showed me a pic of my atlas, which was very twisted up (fairly common for severe TMJ) and so he treated me for that. I was dizzy and lost in space for weeks afterward. In my search for answers, I found that nerve impingement, often near the oxyput, can also cause dizziness.
It took me a long time to get to the road to recovery - I'm finally in phase two braces and feeling a reduction in symptoms for the first time in years. It took seeing many specialists, getting many second opinions and doing tons of research to get here. TMJ is super tricky to treat as best practices are still not agreed upon and so many healthcare practitioner have little understanding of it.
Well I wanted to share some of my experiences with you in hopes that some of it may help...
Wish you well in your recovery
I feel liek I am cosntantly in a drunk daze, and I feel like everything is surreal. 
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