I have a problem with over-heating after even mild, sustained exertion. It can happen even when it is cold outside, it just takes a little longer (not much, maybe an additional 15 or 20 minutes.) First I get very hot and my skin gets red. If I don t stop working my lower back will begin to ache. Following that I get abdominal cramps and diarrhea. Finally, I have muscle fatigue to the point that I have to either lie down or fall down. I have laid down in the snow several times, on the ground on more than one occasion (once right outside the porta potties at a horse show, so you can see it s not as if I have a choice. It was extremely embarrassing.) On that occasion my husband took me to the hospital where they initially thought I d had a heart attack because my blood pressure was so low. This has been going on for at least four years. I am currently limiting my work to short periods, with a cool down and a cold drink between working, but this has really limited my ability to get anything done that requires sustained effort. What the heck is this? And how do I get rid of it?