In Macbeth, analyze Lady Macbeth's sleepwalking in terms of characterization.
Despite Lady Macbeth's early bravado concerning Duncan's murder, the way she shames her husband for his reluctance to commit the murder, and her belittling of him when he initially regrets it, there are some clues that she is not as steel-nerved and ruthless as she'd like Macbeth to think. When she first learns of the Weird Sisters' remarks to her husband, she prays to be "unsex[ed]" and filled "from the crown to the toe top-full / Of direst cruelty" (1.5.48,49-50). Further, she says,
Make thick my blood.
Stop up th' access and passage to remorse,
That no compunctious visitings of nature
Shake my fell purpose, nor keep peace between
Th' effect and it. (1.5.50-54)
She prays to have any quality associated with being feminine removed from her body: she doesn't want to be soft or gentle and kind. She wants to be hard and terrible and cruel. She asks that any feelings of remorse or compassion be quelled so that she is able to go forward with what she plans. Why would Lady Macbeth need to pray for these capabilities if she already felt herself to be cruel and ruthless? She must feel that some remorse or compassion could flare up inconveniently and make her regret her decision or feel guilty about it. In other words, she is not, by nature, evil.
Later, while Macbeth is away, performing the murder, Lady Macbeth says that "Had [Duncan] not resembled / [Her] father as he slept," she would have killed the king herself (2.2.16-17). This implies that she has a certain sentimentality, despite her hopes that she will be cruel enough to perform the murder herself; when the chips are down, she cannot do it. Her "better" feelings seem to overrule the worse when it matters most.
Ultimately, then, when Lady Macbeth sleepwalks and talks, she reveals that those better feelings have not gone away. They have persisted, and her guilt about Duncan's murder—and all of the other murderous acts her husband has performed since—has grown and festered inside her until it has found some release. She can hide it all while she's awake, but she, while she sleeps, those true feelings come out. We see that Lady Macbeth was destroyed by her ambition: she manipulated her husband for personal gain, and he became a monster, and now her conscience cannot support what she has done—and Shakespeare gave us clues about her true character from the beginning.
Sleep is a prevailing motif in Macbeth. Shakespeare uses it throughout the play to show the guilty consciences of Macbeth and Lady Macbeth. At the beginning of the play, after the murder of Duncan, it is Macbeth who is filled with remorse and guilt. He is immediately sorry that he committed the act and cries,
Macbeth has murdered sleep.
Macbeth shall sleep no more.
Yet, Lady Macbeth feels no guilt, no remorse. She assures her husband that "a little water clears us of this deed." She is, unlike Macbeth, thrilled with the anticipation of how their lives will change as a result of killing Duncan.
Throughout the play, Macbeth is troubled with being unable to sleep. Lady Macbeth refers to his bad dreams, and his sleepless nights:
You lack the season of all natures, sleep.
So, it is fitting that when Shakespeare shows Lady Macbeth's collapse in Act 5 that she displays her delayed feelings of regret and guilt through sleepwalking--which signifies a very troubled sleep. As Lady Macbeth sleepwalks, she references many of the misdeeds committed by her husband and especially the murder of Duncan that she had planned. Her sleep in a way was "murdered" too, and the only way for her to regain the peace she once had is to die.
In the play, Shakespeare explores the psychological consequences of committing immoral acts for personal gain. He shows the devastating effects of a guilty conscience through the inability to sleep peacefully.
In my mind, the purpose of the sleepwalking scene is to reflect a level of change within Lady Macbeth. From being seen as a source or origin of evil intent and actions, confident and assured that what was done was needed to be done, and from one who was driven by her "function not being smothered by surmise," Shakespeare intends to create an individual who has been crushed under the weight of evil. The idea of sleepwalking itself reflects an unnatural state. In making her sleepwalk, we can see a couple of things. One of these is that the most natural and peace-like state of slumber is distorted. This might help to reflect Lady Macbeth's own recognition that what was done in the name of ambition is unholy and unnatural. Additionally, it is an indication that Lady Macbeth is coming "unglued." When captured sleepwalking, it helps to bring out the idea that something is amiss in Lady Macbeth. Finally, I think that the domestic purpose of Lady Macbeth's sleepwalking might help to reflect the fundamental state of the marriage at the end of the drama. The notion of sleep between a husband and wife is fairly sacred and absolute. Yet, in seeing her sleepwalk, this notion is disrupted, reflecting the bond between husband and wife is also disturbed, past a point of being fixed without drastic acknowledgement and recognition.