I also have detereriorating muscle pain and weakness, but it is an expected part of my dx as I have hereditary sensory motor neuropathy. (CMT).
I did have an episode where my symptoms all became much worse, as you describe, when I was put on Tricor for high triglycerides. I lost all sense of balance as well. My neuro suggested I might want to stop them, and things improved when I did.
Statins and triglyceride lowering meds can have this effect. Are you taking any?
Even if you have been on them a while, I think they can still create a problem seemingly suddenly, perhaps if your SFN worsened? Lots of people here have experience with them.

Also, does it hurt while you are walking, or do you experience some relief fom it? My legs hurt all the time, and I have trouble standing or kneeling at church, but I find some relief when I am walking, especially in the park or woods. I use two hiking poles, but my morning walk is the high point of my day. I am not sure if it helps or hurts my condition, but I plan to continue as long as I am able.