Many days/nights, for no explainable reason, my nerves aren’t right and I just simply can't seem to deliver my cue straight back and straight through consistently. Due to that, I’m capable of missing absolutely any given shot at any time, no matter how easy. I never experienced anything like that in my younger years. Very strange and frustrating.
It often takes me 2 or even 3 hours of playing before I start feeling any confidence in my stroke. My best tournament play generally occurs when I get knocked in the loser's bracket early, then manage to survive numerous matches in the 1-loss bracket, eventually finding my stroke and confidence.
I had the same problem, and I beat it.
The fact that you gain confidence in your stroke and start shooting better by fighting your way back up through the loser's bracket indicates that your issue is probably not due to physical impairment.
Instead of starting with the drill in the thread I linked to you might want to try one that Tor Lowry had in his 2 hour freebie on youtube - no longer available - but here is the drill on another site:
https://www.cuedrills.com/drills/stroke-drills/tor-lowry-stroke-drill/
The key is to stay relaxed and focused and that is easier to do with this drill because there is no pressure of making a shot. In your case I would simplify it to just piling up the balls at one end of the table and just shooting the same shot over and over for a while.
After you gain confidence you can switch to the full drill but shoot a hundred or so shots first. If jumping to the full drill puts you in the ditch, revert to the simplified version, rinse and repeat. The idea is to achieve a mindlessness muscle memory stroke that you no longer have to think about.
Take your time, make sure your grip stays relaxed at all times, stay down until the ball goes in, make sure you don't change grip mid stroke when hitting the ball (that was part of my problem), make sure your arm is the only thing moving (no shoulder/upper body action!) and do extra warm up strokes at first.
It is a real good idea to standardize your pre shot routine and perform it with each and every shot.
My main issue was a circular problem where I had lost confidence in my stroke and so I was getting down on shots while wondering if it was going to work, which in turn was causing me to doubt my stroke and so on...
I have pretty much conquered that but I had to be, and still am, very tenacious about it. The only way to get rid of a bad habit is to replace it with a good one.