Final answer:
The sleepwalking scene indicates Lady Macbeth's severe mental decline, contrasting her prior strength with her current breakdown. The irony is in her inability to cleanse the guilt she formerly dismissed, reflecting her inner torment over the crimes she encouraged.
Step-by-step explanation:
The sleepwalking scene in Macbeth reveals a drastic change in Lady Macbeth's state of mind. Initially, she is portrayed as strong-willed and manipulative, urging Macbeth to commit the regicide and chastising his hesitations. However, her later sleepwalking signifies that she is haunted by guilt and cannot escape the consequences of her actions. This inner turmoil manifests physically through her obsessive handwashing and speaking of the horrors she's complicit in.
The irony in this change lies in the contrast between her former commanding presence and her current state of mental disintegration. Lady Macbeth, who convincingly argued that a little water clears us of the deed, now compulsively tries to wash off imaginary bloodstains that represent her inescapable guilt. The woman who once emboldened her husband to embrace murder as a means to power is now powerless against her own conscience.