What a fantastic battle! One for the ages indeed. Gonna be hard to fall asleep anytime soon after that one. Looked like Mu was feeling more pressure from this race than Tokyo. I hope she takes a few months off, she deserves it.
She just looks (to me at least) stressed and sluggish and not having fun; her incredible talent let her pull this off but I think you're right. Some time off, process everything that's going on, let some of the pressure slide off. Pretty amazing for someone this young to follow up Oly gold with WC gold, but she's human too.
Starting from the U.S. championship it's clear that Mu is not as fit as last year. There's a very fine line between being in peak shape and losing that edge due to injury and/or illness. She may have missed training time. I think that's what's happened.