Heat stroke might've been an hour to hour issue. But the human body is 60% water. You're not going to sweat out the several kilograms of water required to shift that percentage significantly, even within a whole day.
Yes, a human will die of thirst before hunger, but that still takes days, not hours, and the majority of that liquid loss will be due to urination, not heat related sweating.
The bad feels of hot weather has more to do with the heat itself, and the salts and those electrolytes you're sweating out.