Tell tale heart

My first impression is that the narrator is completely unreliable if not mentally ill. His descriptions of himself and his loathings are exaggerated and manic,

"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."