Act five (scene one) of Macbeth shows Lady Macbeth to be fighting an internal struggle with her part in the murder of King Duncan. Prior to this scene, Lady Macbeth has been far stronger than her husband (even pushing him to murder Duncan and take the crown for himself).
Once Macbeth proves his manhood (by taking control of holding onto the crown), Lady Macbeth no longer needs to be the one in control.
Be innocent of the knowledge, dearest chuck.
With this phrase, Macbeth takes control of his own life (his manhood) back from his wife. No longer does he need her to construct plans which are meant to keep the crown in his hands.
That being done, Lady Macbeth finds the power which she desired no longer necessary. She, essentially, becomes the stereotypical subordinate to her king. The sleepwalking, then, shows how much the murder of Duncan is weighing upon her. As a woman, she is prone to the emotional weaknesses typically seen in women. The sleepwalking denotes her true identity and guilt for the blood which she has brought upon her own hands.
What, will these hands ne'er be clean?
Her statement while sleepwalking shows her subconscious coming forward--forcing her to feel the guilt. Overall, while power-hungry at first, Lady Macbeth is a delicate woman prone to the emotional roller coaster stereotypical of the characterizations placed upon them.