I should have seen it coming. All the factors were there. A dentist visit in the AM and a mouth full of novicane prevented me from eating properly. I started the ride at 1PM, when it was already 85F. I headed north, and had a wonderful tailwind so the first half (distance-wise) of the 55mile ride went really quickly. Then I turned around to head home. It was hotter. The headwind was directly in my face at 20-30MPH. Temps were pushing 90F. I hadn't eaten enough, and, apparently, didn't drink enough. I took a break with 8 miles left, sucked down the last packet of gell, and kepy going. Then it happened, with two miles left. I was climbing the last hill, or trying to, when it felt like a knife in the quads. Both of them. I was off the bike and walking it up a damned hill, something I haven't done since I was a kid, and all due to heat, lack of food, and no powerade, I guess. Anyway, the upshot it that even at this advanced age, there are lessons out there in the heat.
Back on the bike the next morning for a recover ride and all was fine.