An update:
Three weeks ago I went on the SSRI Sertraline at 50mg for three days, after which I halved the dose and continued at 25mg for two weeks in total and then tapered down to 12.5mg for two days and have now abstained.
The first few days I had waves of strong nausea, almost no sexual libido (later returned) and I felt constantly 'up', as you might expect from its stimulant properties. Apart from those, side effects were very tolerable.
After only four or so days, I felt significant improvements. For the first time in a year, simply breathing air felt extraordinarily pleasant. I believe it has fixed my DP/DR and largely my HPPD. Anhedonia is still there to some extent but massively improved; apathy is gone; emotions are mild but present again. A feeling of warmth in my brain returned, whose absence I never acclimatized to. I can do light yawns again.
I don't attribute my recovery up until this point entirely to Sertraline whatsoever and I'd especially advise against using it at an early stage of the comedown. I was extremely skeptical and cautious about going on SSRIs but took a calculated risk based on a range of factors. I'm still not where I'd like to be but I'd like to think I might finally be over the worst of it now. The most major improvements happened markedly, began suddenly and continued slowly to a point then stopped again and for no discernible reason. Around December, I could sense that my brain's pleasure centre was finally rebooting and I think SSRIs were necessary for me to assist the effort for homeostasis. Interestingly, Mirtazapine is still effective but much less rushy and obtuse in its effects as it were prior to SSRI treatment, which I believe is an indicator that my brain is actually processing the chemical rather than just swimming in it. I'm still mongy by average person standards but far out of the deep deep hole from which I began this journey. I am absolutely grateful for any feeling of goodness and visual clarity now.
It's still early days as it's only been a week and a half since I came off the Sertraline so I could easily relapse as we here know all too well happens. But it's given me bounds of hope. I wanted to make sure I wasn't one of those people who inexplicably disappeared off the forum after some respite and provide anecdotal information which is obviously us LTCers bread and butter. Some bizzare and highly irritating physical symptoms which constituted half of my stressors to a debilitating level have subsided which proves I could have avoided a lot of anguish by practicing better mindfulness.
Right now I'd say my worst symptom is TMJ disorder. I've been suffering from a stiff and clicky jaw since the beginning. I've seen a few specialists about it but I've only received blanket advice like 'don't move it around incessantly' which is exactly what I do unfortunately. It's an OCD habit. It's also a constant reminder that I've fucked up despite my recovery in every other respect, it still causes me much concern. Improving it is probably just a case of mindfulness again and hoping for the best it doesn't deteriorate.
Also insomnia and tinnitus are still bad.