I think about this often. I keep a memento mori to remind me: since life is finite, we are all living our final days, it is only a matter of degree.
The best conclusion I’ve managed is not to spend final moments in regret (there are always more things to do, I would try to let go of that). I’ve never met anyone who, in their final days, regretted not working more. I’ve seen people regret not spending more time with people they care about, not developing their own talents, not experiencing (travel, food, cultures, etc.), and things left unsaid (apologies,admissions, etc.).
So I try to do my best at those things, as if living my final days. The first and last things are relatively easy – don’t leave things unsaid, and spend time with people you care about. I guess those are the biggest two I’d spend effort on. I’d perhaps write these things in letters, if it was more practical (although I would make sure they are kind letters – if we leave behind something, why not kindness? All my bitterness can die with me.).
All that being said, an old friend of mine had similar symptoms as you, and it also took a long time to diagnose. Eventually they were diagnosed with idiopathic dystonia, received treatment, and mostly recovered (I’m not attempting a diagnosis here, only telling a story). The medical system can be slow and diagnosing the many things that can go wrong with our bodies is hard. As long as you’re alive, and have not received a terminal diagnosis, a positive outcome remains possible.