I went cycling yesterday and over did it. I got a late start (10am) and ended up coming back over the hardest climb at about 2pm. It must have been close to 100 degrees. I knew it was going to be hot, so I drank as often as I could but that didn't seem to be enough because I started to cramp around mile 45. By the time I got home, I was severely dehydrated and after drinking a bunch of water, I actually had to take a nap to recover. I felt better after that, but haven't been that exhausted in a long time.
It was nice getting out on the bike, but I'll think twice before going out when it's so hot again.