A co-worker of mine "went down" yesterday, in the words of the supervisor. That is, he was overcome by heat stress. Someone found him lying on the ground, shaking, and called an ambulance. He recovered fairly quickly, once they cooled him down, and he should be okay.
It's very hot out there folks, and if you have to spend an extended period of time exerting yourself outside, take precautions. If you wait until you're really thirsty to drink some water, you have waited too long. Try to keep drinking before you get thirsty. This isn't always easy, but it's easier than dying of heat stroke. And wear a decent hat. I'm pretty sure this guy doesn't ever wear a hat, which is just dumb in this kind of weather. I wear a boonie hat with a wide brim and a ventilated crown.
Be careful out there.