I noticed after fasting for a day that I got my energy back as soon as I ate something - even before there was any possible way it was digested.

At that point I decided/realized energy is all in my head, and fasts don't bother me anymore.

It's also true when doing things like moving, or fixing a car: I'm usually very out of shape, and can't even run a city block. But if I need the energy, it's there.