I felt a Funeral, in my Brain

In I felt a Funeral, in my Brain, the speaker creates and extended metaphor of the loss of his/her mind. The funeral represents the end of normal functioning in the brain, as normal functioning of the body ends when a person dies. It seems that this person gradually lost their mind, as shown by the words "treading- treading" and "beating- bearing". It is possible that the loss of her mind could be a very sad realization to which the speaker has arrived because of be comparison to a funeral. The reason for we insanity is unknown, but it doesn't seem central to the overall theme of the poem anyways. Another unclear spectrum of this poem is the random capitalization of words. Sometime this can indicate important words or words with a greater meaning. For example, "As all the Heavens were a Bell". Why is "Heavens" and "Bell" capitalized? My favorite line that Emily Dickinson writes in this poem is  "and then a Plank in Reason, broke," because it very nicely, yet clearly deceives her insanity.