You can be fooled by that because it may appear that they are waking up and just acting a little strange. It's not the only concern, but it's the most important. Use common sense. If you are outside, and working take breaks and drink water every 20 minutes. No alcohol, be careful of medications that reduce your ability to tolerate heat - which means you should be even more careful in warm weather.
Hydration is important.
You can sweat away more volume in an hour than your body can absorb in liquid if you drink it. By taking a cold shower. I gave her liquid Advil and a glass of water. What you needed to do is put that child in a cold tub. Advil and Tylenol don't work unless they have a fever from a virus.