"Come Sleep! O Sleep" isn't your ordinary "Jeepers!-I-can't-sleep" poem. This is a poem about emotional violence. Think about it: civil wars, dart-throwing, and a shield. Usually, our private struggles aren't that bad, but in this case they are. The speaker is unable to stem the tide of violent emotions that are flat out attacking him. Okay, okay—so he's being metaphorical, we get that; but that doesn't change the fact that he gives us a very unsettling description of sleepless and despair.
Questions About Violence
What is the effect of the words "civil wars"? Why not just "wars"?
Why darts anyway? Are they somehow more violent than, say, knives?
Is Stella at all to blame for the speaker's sense that he's being violently attacked? Why do you think so?
Chew on This
Violence doesn't need to be physical to qualify as violence. Emotions can be violent as well, so violent that their conflict resembles an internal civil war (cannons and funny hats notwithstanding).
Sleeplessness can make us feel that we're being violently attacked. Heck, it's just as frustrating as somebody throwing darts at us.