That heat can beat a feller down! Has me before. Cut a trip short on the Pow-Wow Trail here in MN one July (pre-hammock) so hot and humid that butterfly were not flying but flopping! Tons on black flies and more skeeters than I have ever encountered. I blazed out and cut it two days short.
I actually got heat-stroke on the trip and had to lay in the trail and force myself to eat a Cliff Bar and drink. I was solo and found myself staggering off of the trail. Glad I made myself rest.