The poem "One need not be a chamber to be haunted" deals with a contrast between fears caused by external phenomenon and those caused by our own brain. We see this contrast in the first stanza when the speaker maintains that
The brain has corridors surpassing
In other words, what is inside our brain is much more frightening than any tangible thing or place. This idea is further developed in the second stanza in with the "interior" is more dangerous than an "external ghost." The speaker declares that we can arm ourselves against the "assassin, hid in our apartment," but cannot defend ourselves against the intruders of our minds.
Dickinson is vague as to what we have within that is so frightening. But it could be any number of things: regret, guilt, imagination, anxiety, paranoia, fears of loss or death--anything that makes us fearful to continue on with life or reluctant to get out of bed.
Emily Dickinson examines the themes of mental anguish, fear, loneliness, anxiety, and internal conflict throughout her poem "One need not be a chamber to be haunted." Throughout the poem, Dickinson explores two differing types of fears by contrasting internal and external threats. She argues that one's mind is far more frightening than meeting a ghost at midnight, galloping through a dangerous abbey, or being stalked by an assassin in one's home. Dickinson also compares one's mind to a house with haunted corridors. She believes that individuals are helpless against the inner workings of the mind. Dickinson may be commenting on her personal psychological struggles or simply observing the agonizing nature of individuals suffering from mental disorders. Pervasive loneliness and helplessness are also significant aspects regarding personal fears. Cognitive struggles can be a source of extreme anxiety and anguish. Emily Dickinson's poem reveals the terrifying nature of mental illness and argues that individuals should fear their minds more than they fear external threats.