I also have SFN with autonomic dysfunction. Have you been tested for rheumatology issues? You may also have an immune issue that is causing extreme fatigue. I had the same issue and found I have RA, Sjogren's, and CVID on top of the SFN which caused me great distress. I would suggest seeing your Primary to have further testing to see if there is something else. Like me, the drs were looking for one problem but I actually had multiple problems.