I have the same problem in real life. It can be 100 F / 38 C outside, and I will be dry as a bone despite keeping very well hydrated. It really is a very dangerous condition to live with. Which is why I live in a state that has cool springs, cool falls, and very cold winters, rather than where it's always warm. To compensate, I bring extra water so I can pour a little over my head when it gets really hot, and still have plenty to drink, too.

Getting dizzy and nearly blacking out due to overheating is NOT fun.