We spent 4-5 months each summer for six years hitting as many national parks as possible. We had a wonderful time, but at Arches National Park we almost had a tragedy.
I deal well with extreme dry heat; the Spousal Equivalent does not. The day we were at Arches, it was hotter 'n the hinges of Hell. I'm talking waaaaay over 100 and dry like you can't imagine. We have hats and water and figure we're OK for a short hike.
We're tooling along a trail, the SE says suddenly "I don't feel well" and promptly keels over, splat down in the dust. I mean, he looks like he's dead. There's no cellphone service, of course, and I'm pouring water on him and trying to figure how I'm going to pick him up and drag him back down the trail. I'm shouting for help.
Luckily, a group of hikers come around the bend and help out. One of them takes off down the trail to get help and four guys pick him up and start moving back down the trail until we find a rock overhang with a little shade. By then, he's coming to and is doing remarkably well for someone I thought was deceased. After a bit of a rest and a lot of water, we head back to the car just in time to run into a hysterical park trainee ranger racing up the trail who's sure she has a dead body to contend with. We were all happy this wasn't the case. He spent the rest of the day sitting in the truck with the air conditioning running while I went sightseeing.
Of course, he got his laugh on me later when I did a black-out faceplant in the ranger station on top of the Rockies in the national park. I don't do well with altitude (12,000 feet that was) and he does.
Death Valley in August was a bit much for even me.