What does the narrator say when he is crazy in "The Tell-Tale Heart"?

The narrator actually spends a great deal of time assuring us that he is not crazy in this story. He thinks that we will assume that he is insane, and so he is quick to defend himself against the charge. He enjoins us to see how "healthily" and "calmly" he can tell us his story. He says, "You fancy me mad. Madmen know nothing." He believes that he is very intelligent, very purposeful, and very measured, and he thinks these qualities are somehow at odds with mental illness; he doesn't see that he can be all of these things and still be ill.

Moreover, the narrator doesn't recognize that wanting to kill a sweet old man because he has a weird eyeball would also be considered the action of an ill person. He doesn't see that mistaking the beating of his own heart for the beating heart of a man across the room, or, later, a dead man, is a sign of illness.  The narrator assures us that what we think is mental illness is actually "but over-acuteness of the sense[s]." In other words, he thinks that he is just very sensitive and attentive to detail, not that he is insane. Further, he seeks to convince us that he is not mad by pointing out "the wise precautions [he] took for the concealment of the [old man's] body." He takes great pride in his plans and likewise believes that they prove his sanity. The narrator does not realize that he is mad, but he is, and this story is representative of his madness and delusion.