You are on the right track. I'd speculate there are memories from your childhood that could be the root cause of it.
It will take time for things to change. To figure out what is going on and to listen to the messages from your body, but things will get better for you.
It took around 2 years for me (with reading and therapy) to make significant progress, but I had to exist in a world where some of the people who created the original issues were in my life still and were very unsupportive of my new revelations, which made the process harder than it needed to be. The process isn't over for me yet, but the hardest part is over with the PEM disappearing and depression abating.
Please drop me an email (email in profile) sometime, I'd be keen to know how you get on and what you learn.
You both mention self negative talk and for that reason I come forward with this recommendation, but things you discuss (repressed emotions, powerlessness/vulnerability, self-leadership,...) are all intertwined and addressed in the book in an insightful way.
The most important thing is to _experience_ Voice Dialogue (or IFS, which slightly differs in approach), ie. to be in the situation when someone talks to your 'voices'/'selves' and you 'enter' those 'voices'/'selves'. This experience results in a revelation which I tend to call (a deep) insight, no less.
VD precedes IFS (which is not that important) and I have a strong preference to VD over IFS (I would need to read more on IFS and clarify my points, which range from personal to very technical, to justify my preference).
I think most importantly the new connection for me is that i simply get worn down outside or among other people incredibly fast for some reason - same with work projects.
I am still unsure of the actual physiological cause, as it seems to me that i can also get a crash even if i run alone in the woods - ie. no other people, but it's still a "performance" and "you" still judge it with your own mind.
What makes me sure that there is something this is the fact that you have experienced both this AND the feeling of powerlessness - and the paranoia around this - i hadn't really seen this before but i totally also have that - down the fact that i have also been high on new fads, diets, lifestyle changes but only for a few weeks or months before i try something new.
So in short "the crash" is related to feelings of being in control, bodytension and not letting things go properly, instead judging hard, becoming perfectionist and having feelings of "not good enough" - even though i just finished something. Being a hermit with your laptop is fleeing from all responsibility and letting the mind rest, just as the body, and you are probably right that the mind is just as important.
So to sum up mostly for myself. Letting go, being kind on yourself, and being comfortable with "other peoples eyes" around me, appreciating smaller incremental victories, and just as you also mentioned in you first comment - building self reliance is something i have to learn to do. I have probably had a pretty high level of anxiety inside of me that i have ignored like "everyone has imposter syndrome", or "everyone is afraid of getting exposed (whatever that means)", but it wears you down.
Just writing this out is untangling a few things for me so thank again!