I'm sorry you are having this difficulty.

Anxiety of the sort you describe has always been a big problem for me too. And I've overdosed twice on prescription med's.

So I have some idea of what you're going through.
Unfortunately I don't know of any "quick fixes" for this. You mentioned you tried meditation but it didn't work. I'd have to say that meditation has never really been effective as a short-term anxiety relief tool for me either. That's not to say it's not a good idea though. And I would encourage you to stick with it. But it's a long-term process, in my opinion.
Other similar sorts of things I have seen recommended, by members here on PC, would include binaural beats (look this up on the web or check it out on YouTube if you're unfamiliar) & also accupressure for anxiety. (This is also something you can search on the web.) My personal opinion is that one of the best anxiety-busters is plenty of vigorous exercise.
I can't speak for the idea of medications. Any med's I've ever taken have just made me groggy. Likewise, I can't really speak to the question of how to increase your cognitive functioning. I know there are internet games that purport to do this. However, from what I've read, there's no real hard evidence that any of them really work.
At the risk of overwhelming you with reading material...

here are links to a bunch of articles, from PsychCentral's archives, on the subject of how to relieve anxiety along with one on the subject of how to relieve the cognitive symptoms of depression. Hopefully some of the suggestions in these articles can be of some help:
https://psychcentral.com/lib/9-ways-...ere-right-now/
https://blogs.psychcentral.com/chang...itation-fails/
https://psychcentral.com/lib/15-smal...iety-symptoms/
https://psychcentral.com/lib/strateg...ty-and-stress/
https://psychcentral.com/blog/11-tip...anage-anxiety/
https://psychcentral.com/lib/the-pow...reduce-stress/
https://psychcentral.com/blog/3-tips...hrink-anxiety/
https://psychcentral.com/blog/5-quic...xiety-at-work/
https://blogs.psychcentral.com/imper...s-and-anxiety/
https://psychcentral.com/lib/top-10-...s-for-anxiety/
https://psychcentral.com/lib/20-tips...e-your-stress/
https://psychcentral.com/blog/how-to...viate-anxiety/
https://psychcentral.com/lib/strateg...of-depression/
I wish you well...