It is really hard to not think about if he would have blown up this much if he didn't throw a perfect game. I don't care what people say, something like that has to alter your mind-set and way of thinking when you go out there on the mound. I don't care if he's a professional athlete: he's a human, and doing something that unprecedented and prestigious has to get in his head. Before the prefect game, there was zero pressure on him. Now, whether there actually is or not, in his mind, there's pressure now to perform.
I don't know what else it could be. He's not a bad pitcher and he, all of a sudden, didn't forget how to pitch.