Thanks everyone! Still a little sore today, but not as bad as I expected.

Yes. Wikipedia describes it as "In endurance sports such as cycling and running, hitting the wall or the bonk describes a condition caused by the depletion of glycogen stores in the liver and muscles, which manifests itself by sudden fatigue and loss of energy." I had plenty of food (ran out of water for a little while) but I wasn't keeping up with how much I was burning, I guess. I've heard that your body can also switch gears and begins feeding on itself (i.e. starts exclusively burning stored fat) after hitting the wall and then you can get a fresh burst of energy. That's sort of how I felt going into the final 25 miles. Good energy, but my body was screaming at me to stop!