why does heat cause fatigue?

[Dan]

It was a rather warm day today and I was left feeling kind of lethargic. This got me thinking, what is the reason for heat tiring you out?

 

[stryder]

Well, my uneducated guess would be dehydration and the loss of electrolytes due to increased perspiration. When I use to do landscaping it would get up to 90+ degrees in the summer and being out in the direct sunlight all day really wore you out, but once I'd swig down that cold ice water I was good to go...