Since she is sleepwalking and revealing secrets she swore she would not tell, it shows that she no longer has control of her actions and she is now a shell of a person full of endless guilt, which causes the reader to feel sympathy towards her.
Shakespeare creates sympathy here by showing the immense guilt Lady Macbeth feels, even though she did not directly murder someone. Lady Macbeth is aware that no matter what she does, her deed will not be undone and she cannot be redeemed.
