It's over training syndrome, caused by too much training without enough rest. The athletes that try to push through struggle to perform as well.
TL;DR: It’s not good to exercise too much with no rest. Your body won’t actually be able to repair itself to how you were before the workout, let alone improve at all. Someone’s coach gave them a training plan that was bad and caused this.
Thanks. Pretty obvious I would have thought. Or are people just watching to many Marvel/D.C. movies?
For a highly motivated person in their late teens/early twenties, being coached by professionals, and on the path to competing in the Olympics, it may not be so obvious. The transcript is worth a read.