Without having the relevant biological knowledge myself, all I can think is that every part of my digestive system was so primed for use that as soon as I started chewing on something, I guess I felt stimulated in the same way that doing some exercise kind of invigorates and wakes you up a bit. I think the other aspect would just be purely emotional/psychological, in that I was just recieving something that I had really wanted to have for the last 24 hours or so. Perhaps a similar effect happens whenever a biological need is postponed for an unusually long time, like the elation of when you finally get to a bathroom after an hour has passed since you first identified that you need to go, haha!
RE: My first quarterly fast, done!