What is the tone of the narrator?
"True! -nervous- very, very dreadfully nervous I had been and am; but why will you say that I am mad? The disease had sharpened my senses - not destroyed - not dulled them. Above all was the sense of hearing acute. I heard all things in the heaven and in the earth. I heard many things in hell. How, then, am I mad? Hearken! And observe how healthily - how calmly I can tell you the whole story."