I felt a Funeral, in my Brain

One of the things I noticed in Emily Dickenson's I felt a Funeral, in my Brain was that she used each quatrain to represent a different aspect of a funeral.  The first stanza, with its "Mourners to and fro kept treading" (Dickenson, 776), is clearly about the showing of a funeral.  The following section talks about the actual funeral service, as though in a church.  The casket is being moved in the third quatrain.  Church bells are heard at the casket's departure in the forth, and it is lowered into the ground in the last.  It was clear, however, that this poem was not about a literal funeral.  Dickenson uses only auditory imagery in this poem, with not a single reference to sight.  If this person, who is clearly in the casket, can hear, interpret, and understand everything that is occurring on the outside, then he surely can not be dead!  It seems to me that something traumatic has happened to the narrator of this poem.  She speaks of the funeral being IN her brain.  Perhaps she lost a piece of her innocence, or is deeply disturbed by a newly discovered truth?  It could also be that the speaker may have come to terms with the fact that she is mad and can no longer control her brain.