--came on very fast--over the course of hours to days, and continued to worsen for about three-four months, whereupon it plateaued for some months (fortunately, I was getting decent pain relief from Neurontin by then, and had gotten a skin biopsy to confirm damage to the small fiber axons, which was the only test result that indicated anything), and then slowly--very slowly--began to recede.

This is consistent with the (admittedly skimpy) research on acute onset neuropathies of unknown etiology; molecular mimicry autoimmune processes are suspected, though hard to prove, and there tends to be "slow, partial recovery" over months to years. Susbsequent skin biopsies I've had have shown some re-enervation, though I'll probably never get back to my original baseline nerve density. Presumably, the autoimmune attack petered out when there was nothing else to destroy.

It is certainly possible for neuropathies to improve--if there's a direct toxic, nutritional, or metabolic cause to the neuropathy and that is eliminated or controlled, re-enervation can occur. This process tends to be EXTREMELY slow, though--nerves regenerate more slowly than just about any other bodily tissue--and while it's happening, one can get all sorts of weird sensations and pain as nerves reconnect in new patterns and the brain tries to make sense of the new signals. In fact, during the process, which is often described as "flaring", it's hard to know if one is getting better or worse except in long-term retrospect.