Throughout Macbeth, William Shakespeare uses the word "sleep" many times, and often through Macbeth himself. When someone commits a crime, he or she is usually "caught up" in the moment of the deed, and only sees the immediate consequences or rewards; however, later on, he or she will have time to think about what he or she did, and this time just happens to be when the criminal is about to go to sleep. As the play progresses, the word "sleep" is used with multiple connotations to fit the arising scenarios. These connotations are: a state of peaceful rest, vulnerability, and a supernatural state of existence.
Macbeth obsesses over whether or not he will be able to sleep even before he kills King Duncan, because sleep is something that he knows he will need in order to feel peaceful and well-rested. "Nature seems dead and wicked dreams abuse/ The curtained sleep." [II.1.62] Macbeth is describing how he feels that his decision to kill Duncan is already haunting him, and that the world seems skewed because of it. He worries that "wicked dreams abuse the curtained sleep," or that his dark and murderous thoughts are disturbing his own rest. Macbeth is talking about sleep as something precious, peaceful, and sought after, which is evident because of how worried he is; he wants an uninterrupted period of rest, but he is afraid that it'll be out of his reach if he kills Duncan. Once he actually kills Duncan, Macbeth starts hearing voices inside his head: "Sleep no more!/Macbeth does murder sleepthe innocent sleep,/ Sleep that knits up the raveled sleave of care/, The death of each day's life..." [II. 2.47] Here, sleep is being used in a positive, restorative sense. It's what rejuvenates men and women, yet Macbeth has "murdered sleep" and cannot rest because he is guilty of a heinous crime. Macbeth is truly worried that he will not be able to reach a state of peace again because King Duncan's murder is haunting him.
Sleep is also used to symbolize a state of vulnerability, or an openness to being attacked. Obviously, one is much less aware, if aware at all, of his or her surroundings when he or she is asleep, just as King Duncan is when Macbeth and Lady Macbeth are plotting to kill him. "When in swinish sleep/ Their drenched natures lies as in a death/ What cannot you and I perform upon/ Th' unguarded Duncan?" [I.7.77] Lady Macbeth says this, assuring Macbeth that the guards in Duncan's room are fast asleep, therefore leaving Duncan unguarded and vulnerable to their attack. The phrase "What cannot you and I perform" roughly translates to, "We can do anything we want to him," in other words, kill him. Keeping in mind that Duncan too is asleep during their plotting, Macbeth and Lady Macbeth know that he would have no intimation of an attack until it is too late, using sleep in the most vulnerable sense. Lady Macbeth would probably reason that when one is asleep, one might as well be dead, for he or she is unable to defend him or herself. The only difference between a corpse and a sleeping person? One who is asleep can wake up; a corpse cannot.
The third way that sleep is used throughout the play is a state of supernatural being. To start things off, this is the most obscure use of the word in Macbeth, and it happens to concern Lady Macbeth more than Macbeth. "Yet all this while in a most fast sleep," says the gentlewoman[V.1.8-9]. The gentlewoman is explaining Lady Macbeth's nighttime sleepwalking rituals to the doctor, telling of how she writes a letter in her sleep and tries to wash her hands. In a way, Lady Macbeth is living in a dream and believing she is doing one thing when, in reality, she has no idea that she isn't really washing her hands. This is likely the result of Lady Macbeth's suppressed guilt for provoking Macbeth to murder King Duncan; and look, she can't sleep peacefully, either! Here, the connection is drawn between the peaceful connotation of the word and the supernatural. Like Macbeth, who could not rest peacefully because of his actions, Lady Macbeth cannot rest either, and she is living in a dream every night.
Additionally, the entire play turns into a "dream" for Lady Macbeth because she gets what she wanted, or what she thought she wanted, once Macbeth rose to power. However, Lady Macbeth isn't asleep all the time, but the doctor hints at the fact that she is living in a dream-like state by saying, "Yet I have known those which have walked in their sleep,/ who have died holily in their beds." [V. 1.62-64] This can be interpreted as a metaphor for Lady Macbeth's "new life." She is walking in her sleep, in a sense, by living out her dream as the Queen of Scotland, but this life is just as unreal to her as her nighttime adventures. When the doctor remarks that he has known those who have "died holily in their beds" he may be foreshadowing Lady Macbeth's demise, for she is "walking in her sleep," and will soon die. The doctor suggests that she is going to die in this dream.
In conclusion, Shakespeare brilliantly plays around with the word "sleep" by using it in ways that are both obvious and hidden, but he also makes the audience think about their own definitions of sleep. From the play, the audience is lead to believe that although sleep is precious, it is something that only comes easily to people with a clear conscience. In Macbeth's case, he cannot sleep until Macduff kills him. He loses something valuable that is often taken for granted because of what he has done. Shakespeare chose to repeatedly mention sleep because, whether it be at the end of the day or the end of one's life, everyone eventually goes to sleep, yet Macbeth gives the reader a better idea of how valuable it truly is. He wanted to make his audience aware of how much they may be taking for granted when they go to bed each night.