Not really sure he's losing his mind, I think it's more just that the public facade slipped, and the media-savvy veneer was peeled away for a bit, probably as mych due to frustration because Usyk was just too good again. Stress and anxiety are never good, but he doesn't have to worry about paying his mortgage or energy bills like the rest of us unwashed masses.
No and neither should he. AJ fights everybody and tries to avenge his losses asap, if every champion was like him the sport of boxing would be in a far much better place right now.