The next morning, the doctor tells Mishima that he's fine. He's just not feeling well. Mishima is blushing, pooping, and generally behaving like a normal person. The doctor tells him that his condition isn't getting any better. He says that he has been studying human emotions, and he warns Mishima not to get too attached to the idea of being a human being, because it's not necessarily good. You might feel happy, sad, disappointed, and so on, but you'll eventually get to the point where you're going to have to deal with all of those emotions. The only thing that's keeping Mishima from getting better is that he doesn't want to be "the ideal of you" , because that'll make his condition worse. He leaves the hospital and dies.