Emily Dickinson is my all-time favorite poet, so it is a joy to help you with this question! The poem "I Heard a Fly Buzz—When I died" seems to be focusing on the literal moment of death for the speaker. A poem that I would compare it to in terms of the themes of death and dying would be "I felt a Funeral in my Brain."
In the poem "I felt a Funeral in my Brain," the speaker seems to be at her own funeral, after her death. The speaker comments about the mourners moving "to and fro" in the first stanza and then goes on to describe the funeral service and eulogy in the second stanza. It is almost as if she is watching her own funeral as she states,
A service like a Drum—
kept beating—beating—till I thought
My mind was going numb.
She goes on...
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