Hi all, @roxannelee mentioned that she had had a "sweat test" done, along with other autonomic testing, and everything was negative, so I wanted to share my experience. Unfortunately autonomic testing alone, including the "sweat test", doesn't seem to diagnose what's wrong with our autonomic nervous system. When I had that testing done at Mayo, it was all negative. But I had a previous tilt table test that had me stand for 15 minutes instead of tilted for 10, and I passed out (heartbeat stopped briefly) at minute 12.

The sweat test they do for autonomic testing measures nerve conduction, not disorders of the sweating system itself. The test we need for temperature regulation issues is called a Thermoregulatory Sweat Test, and apparently not many places do it. I had it done at Mayo in Rochester. They put you in a sort of sauna, cover you in a powder that changes color with moisture, add a sensor that measures your body temperature, and then gradually increase the temperature and humidity. It's not the most comfortable test ever, but it's not painful. In my case they found I don't sweat over 85% of my body. So when I get warm and/or exert myself, my body temperature goes up - sometimes as high as 101. Then as I start cooling off, I feel terribly hot.

Not many clinics do the Thermoregulatory Sweat Test, and you may have to ask for it specifically, since it's not commonly done. But it will detect if you sweat too much or too little. If you sweat too little, unfortunately treatment is "nonclinical" - you basically have to keep yourself cool with neck fans, wet T-shirts, staying in air conditioning, etc. If you sweat too much though, there are medications they can give, so I recommend the testing if you are having trouble with that.