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.