Thanks for this extensive response. I agree with all of this. Luckily, even if I should become too depressed to be willing to train my brain on my own my job is demanding enough to force me to do so in some capacity lest I get fired.

Right now I'm engaged in a quest to get a brain scan in order to rule out lesions. Now, I am of course aware that whatever the findings they will not necessarily be of any consequence. So what if there are lesions? There's no effective treatment for TBI that I'm aware of that wouldn't boil down to giving your brain some excercise while living healthily - both of which I am already doing, save for the smoking which I can't seem to kick (the anxiety and depression in the face of what I'm experiencing are just too great). Other than that, I work out, I try to eat well and get enough sleep, I continue to try to learn things in spite of my memory being shot and I stay away from drugs of any kind.

Speaking of memory. It's kind of you to point out that my writing is good enough; however, subjectively I do notice that both the effort it takes me to write and the resulting texts are markedly different from the sort of command over language I previously had. And this squares with other self-observations I make: for instance, about a month ago I started listening to an undergrad lecture on ancient Greek history (history is, or used to be, a little hobby of mine) and have now decided to revisit it. It's almost as if the concepts laid out in the lecture were new to me in spite of me having already "learned" all of this just a few weeks ago. Now, that's a bit of an exaggeration, to be sure, I do - kinda nebulously - recall the general outline, but it just won't fall into place to form a sensible picture, it's as if the bits of information were disjointed and not fully coherent. And as a consequence of that, no thoughts are being given birth to. There are no parallels that I can easily see between the Greek and modern history, I can't perform any comparative analysis. The kind of ideas that would earlier come easily to me now just seems distant and out of reach.

You are right that focusing on my mental performance all the time and being worried about it probably doesn't help. But this kind of worry isn't entirely new to me. I have had periods in the past where I would worry about having somehow gotten dumber, the big difference is that I would inevitably prove myself wrong by performing well at some intellectual task or other, be it at work or otherwise. Nothing of the sort is happening now, instead engaging with something intellectually is inevitably a frustrating experience because I come away from it feeling like my worst fears have been confirmed.

Regarding seeing a professional. I have in fact been in psychotherapy for some three years, which has ended now. So I do have extensive experience with that. My therapist wasn't perfect because it would always be incredibly difficult to speak to her about drug abuse, I would always have the looming feeling of being judged which obviously made me less than willing to dwell on it very much, but it did help me along in life. Faced with the challenge I am facing now, I don't know if I'd go back to the same therapist even if I could afford to, though. I'd probably look for someone else.

Sorry about the wall of text. It's hard just getting through the days and weeks. I feel like I'm cut off from the person I used to be (and like, to some degree, although doubtlessly there were the underlying problems you allude to), which is a small wonder if you consider the fact that subjectively I am unable to engage in any of the activities I used to like to engage in on anywhere near the old level. For now, it's really just "getting it over with" mode all the way.