I'm afraid to say this fatigue issue would not be an issue but for the shock of the rigors of the job. How can this be?
Not saying this just to throw dirt at the President, but all accounts indicate it is true: he has never had to work hard in his life - except perhaps at Harvard. Whether it was the status, a salve for his own insecurity, the fancy house, airplane, and perks, or the mistaken notion he would be a ruler rather than a president of a free constitutional republic -- he clearly underestimated the job.
And he had to take several breaks to recharge.
He'll end up with some "medical issue" and quit before his first term is up, and then be lauded for his martyrism.