If understand correctly, cortisol is pretty much a stress hormone. And your adrenal fatigue is actually a stress disorder, I don't know if anyone has explained that to you. You stress out and your body asks for adrenaline and so it pumps it out in response to stress, but it can't make enough to respond to all the anxiety felt. So that's when you get the fatigue. When you feel energetic, that's probably when your gland is ready with the adrenaline to give out to the rest of body. But it should be released slowly throughout the day and shouldn't really get depleted like it does.

But I hope you know 3x more about adrenal fatigue than I do, I really hope that's redundant info for you. Or maybe I'm flat out wrong.

I quit caffeine because it increases cortisol and, if I remember correctly, it creates more adrenaline (norepinephrine) receptors and therefore builds an adrenaline tolerance in your brain. Anyway, it seems like the two are related and adrenaline is a much needed chemical that keeps us energetic while cortisol is more linked to stress (which we need some of, but not as much as we get with anxiety).