Biked ~2 miles to the gym and I was drenched when I arrived

yeah I was out in similar (higher heat index but lower temp) weather and I thought I was doing good, taking it slow, covering my face from the sun, drinking some water and gatorade

But after I got back inside I felt really faint for a few mins.

2 years ago I did basically what you did, but on a bike. brand new bike, had to take it for a ride, almost couldn’t get up the stairs to the door when I got back.