The comments that Rob and Mark made are on point.
If you have been eating very clean for a while i.e. more than a week. Leptin can be depressed, having a cheat meal(s) can help it "bounce" back.
Everyone nowadays is used to using carbs as an energy source. It takes a few weeks to get fat adapted, and in the beginning you won't feel great.
"And for crying out loud. Don't go into the pain cave. I can't stress this enough. Your Totem Animal won't be in there to help you. You'll be on your own. The Pain Cave is for cowards.
Pain is your companion, don't go hide from it."