The Patient of the Week was a knight at a pretend renaissance fair. In his mind, though, this was a real job. The guy wasn't so much crazy as he was into the idea of being a "knight." He thought it gave him solid values.
But it also gave him a major illness because he actually camped out on the fair grounds and did anything the "king" said, including eating strange items before various duels. Turns out, the knight was in love with the king's fiancee, but too afraid to do anything about it. He didn't consider that honorable. Yet this knight had no problem taking steroids in order to be better at his job.
That was the cause of his sickness. Thirteen summed it up well when speaking to the knight near the end of the hour: You're an idiot.
The most entertaining parts of the episode centered on House trying to deal with Wilson's new girlfriend, Sam. She's his first wife. House didn't want to see his friend hurt again, so tried to make things awkward between the pair by bringing a transvestite to dinner as his date. But that guy just got along well with Sam. Even after House made his intentions clear to Sam, she visited him in his office.
She asked House to simply give her and Wilson a chance. House bristled, but the talk seemed to work. He didn't open a confidential package that Lucas had gathered together on Sam, instead throwing it out and settling for a dose of Ibuprofren. He's gonna try to be a good, normal friend to Wilson.