This Being of mine, whatever it really is, consists of a little flesh, a little breath, and the part which governs.

Taken apart, a person comes to very little: a body, a breath, and the part that decides. The first two you share with every animal, and they are largely out of your hands. The third is small and the only place where anything is up to you, which argues for spending your attention there.

When you are worrying about how you look or feel, sort it into those parts. Some of it is body and needs sleep or a doctor; some is the governing part and needs a decision. Confusing the two is why people try to think their way out of tiredness.