I have muscle wasting but it is due to the large fiber neuropathy, hereditary. I have not heard of it being related to SFN. I have SFN as well. Have you had an EMG/NCS ? Have they ruled out large fiber?
Also if it is due to the neuropathy it is usually a slow process. What is happening to you sounds very scary. Is there any genetic history of something like this in your family? When you say full body, I take it you do not mean just arms and legs which is the usual progression. How far does your numbness extend?