Final answer:
Poe described sanity as horrible because he believed in a dark and despair-filled world. He saw sanity as false hope contrasting with the bleak reality of life. It is uncertain if Poe slipped into mental illness toward the end of his life.
Step-by-step explanation:
Edgar Allan Poe described sanity as horrible because he believed that the world was inherently dark and filled with despair. He saw sanity as a false sense of hope and positivity, contrasting with the bleak reality of life. In his letter, Poe expressed that he became insane with long intervals of horrible sanity, suggesting that his moments of sanity were filled with the awareness of the cruel and hopeless nature of existence.
As for whether Poe had actually slipped into mental illness toward the end of his life, it is difficult to say with certainty. However, it is known that Poe struggled with emotional and psychological challenges throughout his life. He had a history of depression, substance abuse, and personal losses, all of which could have contributed to his mental state.