The short version is, If you want a prescription for building stamina, try accompanying a six-year-old on a 24-hour fasting cure test for hyperinsulinism.
The long version is, You will wear yourself out on Disney movies from the handy and unlimited player above the child’s bed: movies mixed into and between Candyland, I Spy, drawing-and-guessing, and surreptitious breaks for your own food and sanity. And endless blood draws. He will do better than you think he will, and you will bond with him and be so proud of his courage.
And the price you will pay for twenty-four hours of Disney is the dumbest of the songs stuck in your head on repeat for a week.