Macbeth shall sleep no more

In the scenes before and after the murder of King Duncan, there are many references to sleep. Guilt, fear, evil and murder all manifest themselves in the characters as the inability to sleep.

In the introduction of Act II, Banquo, while walking with his son Fleance, senses the impending murder of the King. He feels heavy "like lead" with exhaustion, yet cannot sleep. Macbeth then runs into Banquo, and after wishing on another a good night, Macbeth proceeds to the King's chamber. It is when he is alone, trying to gather his courage, he has his first hallucination of a dagger, pointing towards the room of Duncan. This is the first sign of Macbeth's degrading mental health.

After the murderous deed, Macbeth returns to his wife, nearly traumatized with what he has done, and claims he heard a voice cry:

Methought I heard a voice cry, “Sleep no more!
Macbeth does murder sleep”—the innocent sleep,
Sleep that knits up the raveled sleave of care,
The death of each day’s life, sore labor’s bath,
Balm of hurt minds, great nature’s second course,
Chief nourisher in life’s feast.

Macbeth's paranoia has already begun to set in, and feels as if he will never rest in peace again, after murdering Duncan in cold blood. Sleep is described as knitting up skeins of care, perhaps this is a metaphor to say that when it seems as if we have endless problems, we should "sleep on it", to help put things into perspective. Macbeth also compares sleep to a soothing bath after a day of hard work, and to the main course of a feast. To Macbeth, sleep is not only a necessity of life, but something that makes life worth living, and he feels that when he murdered his King in his sleep, he murdered sleep itself.

The murder of Duncan will never rest with Macbeth's conscience, and it will slowly destroy him. 

Although Macbeth is a seasoned warrior, quite used to the blood and death of war, the murder of Duncan goes against all of his moral code. Duncan, an old, well-favoured king, is vulnerable, and asleep. He could not fight back: sleep is associated with vulnerability and innocence. 

This point can lead back to George Orwell's 1984, where sleep betrays the unconscious thoughts of an individual. After Macbeth murders the king, perhaps he feels he cannot trust himself to rest, in fear of betraying himself. This is relevant later again in the play, when Lady Macbeth begins to sleepwalk.

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Even though I haven't murdered anyone in their sleep, I can make personal connections to how Macbeth is feeling. It's hard to sleep when something bad has happened, or you are anticipating the next day. Often times it is difficult to put thoughts away for the night, even if we wish to "sleep on" important decisions in our lives. 

The unrest Banquo experiences is not a phenomenon known only to literature. Frenzied ants prior to a rainstorm, elephants moving away from coastlines before tsunamis, and Galapagos turtles moving away from volcanoes days before major eruptions. Maybe there is something to pathetic fallacy! Not a personal connection, but animals are cool. 

Macbeth and Banquo meet the Weird Sisters (1.3)