Yeah, PMR got stuck over in "rheumatica" territory because AFAIK no one knows what causes it, so why not call it auto-immune. The treatment is a steroid, prednisone, and AFAIK no one knows why that works either. As long as one doesn't get giant cell arteritis, it's no big deal. Otherwise, it's otherwise. A weird note is that about when I got my first case of it, a riding buddy, 10 years younger, also came down with it. Huh. But it's definitely associated with a big drop in one's parasympathetic nervous system activity and hence an increase in inflammation. (I think that makes sense, but I'm not a doctor). "Polymyalgia" means that everything hurts, literally your muscles, but joints also. Usually a geezer disease. My WAG is that it's associated with low blood levels of choline. I don't consume a lot of eggs and no meat. After that last bout, I started taking a scoop of sunflower lecithin (~400mg choline) every morning, haven't had that problem again.

Digression . . . but just another good use of HRV. Keeps track of all sorts of things.