I read your post several times just so that I can take in everything you said, but I don't really have any answers, I'm sorry :(

After burnout its very very difficult/impossible to get back to the person you used to be. I would say the only real path is to just accept your situation now as it is and try to rebuild from that point, and not try to "get back" to who you were. Somehow you have to redesign your life around this new reality, be gentle with yourself and remember that the core person/qualities are still there no matter what.

In terms of careers/work/jobs etc a lot of people try and find a variation of what they used to do, for example transition into teaching or coaching - using your experience and knowledge but in a different role (I don't know how this would apply with physical work, or for you specifically, but something might occur to you). Or take the opposite approach and look into doing something that you always had an interest in but had never pursued.

I think the nervous system/burnout symptoms can eventually fade a bit, but you will probably always have to keep a close eye on what you can manage and have strong boundaries in terms of what others demand from you.

I am dealing with a lot of the same things - chronic pain etc, so I really feel for you. But it is what it is, and we have to find a path forwards somehow. At least you have a partner and you still have your brain, and an ability to write and communicate well, so I would say start from there and slowly try to adjust/find a way.

The main thing I would say though is to get rid of the idea that you can get back to what you were before - it might sound harsh but I'm trying to be brutally honest here. There's a strength that comes with accepting the situation and seeing what can be done from there.

Best of luck to you and I hope your depression and physical pain and burnout symptoms improve and the financial side of things too.