What does this poem mean? (William Shakespeare)?

I understand parts of it, but what is the meaning to this poem?

"I have not slept

between the acting of a dreadful thing

and the first motion, all the interim is

like a phantasama, or a hideous dream:

The Genius and the mortal instruments

are then in council; and the state of man,

like to a little kingdom, suffers then

the nature of insurrection."

-William Shakespeare, Julius CeaserWhat does this poem mean? (William Shakespeare)?
The lines are spoken by Brutus after he has joined the conspiracy against Caesar. He says that the time between imagining a "dreadful thing" (in this case, murder) and actually carrying it out is like a nightmare; the mind ("Genius") and the body ("mortal instruments") are debating with each other (as politicians do when they meet in a "council"), and it's as if there were a civil war or revolution going on inside him.What does this poem mean? (William Shakespeare)?
I do not know. I also have been trying to find the answer but failed.

Edit: I think Dude the Obscure has it right. I remember seeing some of Brutus in what I was reading. Also that Julius Ceasar used poems in a way no other did.What does this poem mean? (William Shakespeare)?
sounds like the person he is talking about has a guilty conscious.