> And I started taking antihistamines daily.
Antihistamines can make you drowsy, ie. "brain foggy": (Quoting the web)
Side effects of antihistamines
* sleepiness (drowsiness) and reduced co-ordination, reaction speed and judgement – do not drive or use machinery after taking these antihistamines.
* dry mouth.
* blurred vision.
* difficulty peeing.
I take them sometime myself (for the same symptoms as the article) and I really notice the drowsiness - even though it differs from time to time. So I really limit usage.
> Even my lifestyle in my early 20s was a confounding issue. Did I party too hard? Did that era of my life alter my brain chemistry in a way that made me irreparably damaged?
Long-term effects of recreational drugs use (this includes alcohol I would say) have be studied quite a bit I believe not much last-long effects have been found. So don't worry about it, it does not alter your brain permanently.
Finally I like to say that what helped the author a lot is just a shift in focus to personal well-being. Any shift in focus helps in most cases. Taking up dancing, playing guiter, camping, whatever, can also make you feel like you can breath again. Hyperfocus, on any kind of activity, can be damaging in the long run for most people. Variety is the spice (& fresh air) of life.
But note that hyperfocus includes hyperfocus on personal health, well-being and mental health issues, etc. This can also be damaging and anxiety inducing, as you try to start "fixing" everything and trying to "understand" all your root cause in a infinite loop, start comparing with others, etc. So limit the time spend there as well, I would say.