If we had a poll I would vote heat stroke.
I have hiked many desert trails over the years, and I know that heat exhaustion can occur very suddenly, and once it sets in it can affect decision making. Heat stroke can soon follow.
A hike seems very doable in cooler morning temperatures but the situation can quickly go bad when the temperature spikes, especially when you have an uphill climb.
Years ago on one of my desert hikes I made some bad decisions when I became overheated. I couldn’t figure out if I should go backward which was a longer distance or keep going forward, which was shorter in distance but uphill. I didn’t want to drink the last of my water because I thought I should save it because I still had so far to go. At one point I thought I could see shade off the trail when there was none. I reasoned if I closed my eyes and rested for a few minutes I would have the strength to continue hiking.
I managed to hike two more miles that day and made my way out, but a couple other hikers in the area had to be rescued.
I understand how quickly and unexpectedly heat can overtake even experienced hikers, and it affects decision making.
Incidentally, on my most recent desert hike my companion and I passed two different couples who were hiking with babies, on a very strenuous, mostly uphill trail, in the mid day heat.