I am going to a new neurologist and he is going to test me for this. There are several rare diseases that cause this, but mine is probably caused by hepatitis C, mercury toxicity from my fillings, or herpes. The symptoms are: Low blood pressure, orthostatic hypotension adrenal-hypothalamic-pituitary dysfunction low body temperature intolerance to heat or cold bladder dysfunction digestion problems (IBS, diarhea, constipation, bloating, etc) There are probably more, these are the ones I have. I am hoping that I can get rid of the cause and it will go away. But there are some very rare diseases that cause this, so if you have these symptoms, please get it checked by a neurologist who specializes in autonomic neurology. Some of the diseases are fatal if left untreated and mimic CFS, FMS, parkinson's.