I no longer go to a neurologist. We know my small fiber neuropathy is from celiac disease (at one point they suspected it was from my primary immune deficiency) and once I figured out my diet it flared down completely. I had not had a flare in months, maybe even a year or more, before getting the vaccine.
The small fiber neuropathy flared with the first shot but went away. It flared with the 2nd shot, and has diminished, but I am still experiencing a flare. Weirdly, I have pain in my small finger joints now - which had previously not been affected by my small fiber neuropathy. My normal areas of pain from small fiber neuropathy are all flared down now, but my small finger joints are still being affected.
We have moved and I no longer have a neurologist nor do I think I need one currently, or I would ask a neurologist. I did ask my immunologist (well his staff) and my PCP. I also talked with folks at The Immune Deficiency Foundation. They were all aware of neurological flares. They felt the risk, in my case, of not getting vaccinated outweighed the neuropathy - in my case. They said I could be put on Gabapentin or some other medication I have now forgotten the name of. I declined, hoping the neuropathy would flare back down again. It has. It has flared down almost entirely, but I worry about getting a booster. I really worry about getting frequent boosters. I am positive it will flare up my neuropathy. The question is how badly will it flare. It has been awful in the past. It was so bad that it felt like I was walking on glass, I could not feel part of my face, I got burning and stabbing pains. It felt like someone was sticking needles into my toes. Some places felt numb. Anyway, when all that flared down completely for all those months - well I felt like I had been given my life back. I had other problems from untreated celiac disease and those improved as well. Anyway, to risk my health now, because of a booster is a weighty decision. I am jealous of all the ground I gained back. Still, I know the risk of actually getting the virus. It is quite the dilemma I find myself in. My husband is so worried about my immune deficiency (I have something called common variable immune deficiency - although I am borderline at this point so not being treated, just monitored). He worries what the virus will do to me. I think my doctors are in that camp too. So, I will probably get one booster and then hope for the best. I am terrified, though to be frank. My best friend thinks I am a moron after getting the 2nd shot. But, it is my decision.
I hope this helped. I am afraid my situation may be too different from yours to be much help.

My first two shots were Pfizer which increased my pain tremendously so I opted to get the J&J for my booster in October and I’ve been fine. I was so happy when they ok’d mixing vaccines.

My PC doc is not aware of any adverse effects of covid vacs to neuropathy.