I felt a Funeral, in my Brain a second time

"And when they all were seated, A Service..."

I would like to expound on the motivation in choosing the metaphor of a funeral to describe a permanent lapse in sanity.  The first, most obvious reason is that a funeral is an easy way to visually represent the passing of something.  I think there is more to it, though.  In a funeral, the loved ones gather around to grieve and to accept together the death of someone.  Usually, when someone dies, their loved ones are initially in a state of disbelief.  The mind can't contemplate something so significant happening in such a small amount of time.  I think the speaker had been, prior to this funeral of the head, experiencing a growing mental turmoil, showing that some sanity had already diminished.  The funeral, though, represents the ultimate absorption of the fact that sanity has been completely breached.