--and apparent autonomic problems like that, one tends to think this is either a disease of the central nervous system, such as MS, or possibly a body wide peripheral neuropathy of autoimmune or toxic origin (or, somewhat less likely, a metabolic or nutritional origin).

This would likely be beyond the scope of the average neurologist as well--is it possible for you to get a referral to one at major teaching hospital or research center, at which there would be more testing possibilites? (I would hound my current doctors to do this.)