In act 5, scene 1, Lady Macbeth is shown sleepwalking, during which time she is fixated with the act of washing her hands, convinced that they are stained with blood. As she sleepwalks, she can also be observed speaking to herself (and it is through these words that Shakespeare allows us a glimpse into the state of her mind).

Ultimately, by act 5, scene 1, Lady Macbeth is shown overcome with guilt. She had previously assisted Macbeth (and even drove him on) in his murder of Duncan and usurpation of the throne. However, it seems that during this earlier part of the play, she had underestimated the degree to which these actions would later weigh on her conscience. Furthermore, note also that, in this scene, her guilt extends beyond her role in that initial murder of Duncan: thus, in her utterances, we observe Lady Macbeth making reference to the murder of Lady Macduff:

The thane of Fife had a wife: where is she now? (act 5, scene 1)

What we observe in this scene is a window into a tormented mind, overcome by guilt for her and her husband's actions. Macbeth, as a play, does have a psychological component to it, as it follows the psychological repercussions that the act of murder has on its perpetrators: while Macbeth is pushed further into bloodthirsty megalomania, Lady Macbeth is tormented by her guilt.

Lady Macbeth's sleepwalking, and specifically her actions while sleepwalking, show us that her conscience is heavily burdened by what she's done. She says, "Here's the smell of the blood still. All the perfumes of Arabia will not sweeten this little hand" (5.2.53-55). Of course, she cannot actually still smell Duncan's blood on her hands, but she seems to dream it or hallucinate it there, just as Macbeth hallucinated the dagger covered in blood prior to murdering the king. He suffered, then, from a "heat-oppressed brain" just as Lady Macbeth seems to be suffering now. She even seems to know that she helped to create Macbeth as the monster he's become. She says, "The Thane of Fife had a wife. Where is she now? What, will these hands ne'er be clean?" (5.2.44-45). She must suspect that her husband is responsible for the death of Macduff's wife and children, and she connects Lady Macduff's murder to her own sense of guilt through her question about her dirty hands. She is burdened by terrible guilt, and this is weighing heavily on her conscience.

In act 5, scene 1, the Doctor and Gentlewoman witness Lady Macbeth sleepwalking at night. Interestingly, Lady Macbeth is seen excessively rubbing her hands while speaking about the amount of blood at the scene of Duncan's murder. After Lady Macbeth exits the stage, the Doctor tells the Gentlewoman that the queen needs a priest more than she needs a physician. Before the scene ends, the Doctor instructs her to remove anything Lady Macbeth might be able to use to harm herself.

Lady Macbeth's sleepwalking indicates that she has a guilty conscience and is slowly losing her mind. The fact that she is washing imaginary blood from her hands reveals that she feels guilty for participating in King Duncan's murder. Evidently, the queen is not stable and is suffering from a tortured soul. She is filled with guilt, anxiety, and fear, which is why she cannot rest peacefully at night. Her husband is also becoming increasingly distant and tyrannical, which further isolates Lady Macbeth and has a negative impact on her mental state. Overall, her sleepwalking indicates her unstable mind and reveals her guilt. Later on in the play, the audience learns that Lady Macbeth commits suicide.

In the play "Macbeth" by William Shakespeare, the author shows us what happens to a person's state of mind when they step over the boundaries of right and wrong in order to get what they want. We must remember here that later in the play Lady Macbeth is on her own, and more alone and isolated than she is at the beginning. So her state of mind is one of loneliness and being isolated in her feelings of guilt and axiety or terror over being found out and caught. At the beginning of the play she was acting in league with Macbeth - even directing the action. He then goes off like a loose cannon heading in wild directions where he does not want to be followed, even by his wife. He is totally disocciated from her and cold. Alone,guilty and with no-one to unburden to - she sleepwalks and takes her own life.

Lady Macbeth's sleep walking, and what she does and says while she is walking in her sleep, show that she feel very guilty about all the things that she has helped to convince her husband to do.

The most obvious example of this is her compulsive hand washing.  She keeps trying to clean herself and yet the spot will not come out (since it's only in her mind anyway).  This shows that she is not able to overcome her guilt.  She feels that her guilt cannot be washed away.  This is going to lead her to kill herself later on in the play.