What role does mental illness and madness play in Macbeth?
After Macbeth kills King Duncan, his mental health begins to deteroriate. He tells us in this quote that after Duncan's murder, he is outside of the nourishing effects of sleep. By the time that Macbeth arranges for the murders of Banquo and Fleance and then Macduff's family, he has lost all of the comforts that humanity needs to survive.
The ability to sleep, eat, peace of mind, the company of friends and loved ones.
"Still it cried, 'Sleep no more!' to all
'Glamis hath murder'd sleep, and therefore
Shall steep no more, Macbeth shall sleep no
more!'" (Act II, Scene II)
As a price for his actions, his evil deeds, murder, hiring murders, Macbeth surrenders his mind and soul. His mind is corrupted with anxiety and paranoia; his soul is tormented by a guilty conscience.
Lady Macbeth, surrenders her mind, towards the end of the play, at last showing remorse for her role in Duncan's murder. In Act V, Scene I, she utters her famous lines about her blood stained hands, fearing for the consequences of her actions.
"Out, damned spot! out, I say! One;
two: why, then, 'tis time to do't. Hell is murky!
Fie, my lord, fie! a soldier, and afeard? What
need we fear who knows it, when none can call
our power to account? Yet who would have
thought the old man to have had so much
blood In him?" (Act V, Scene I)
The most blatant example of madness is in Lady Macbeth's deteriorating condition. Her doctor says she has a "great disturbance in nature" and an "infected" mind (Act V, scene i). He tells Macbeth that "she is troubled with thick-coming fancies,
That keep her from her rest." Her guilt over the death of Duncan and the futher exploitation of Macbeth's power have caused her to become consumed.
We see this tendency towards mental instability in Macbeth, as well. First, it manifests like Lady Macbeth's and stems from guilt. He is tormented by the ghost of Banquo, feeling too guilty for having killed his friend. Lady Macbeth's cure for her infected mind is to kill herself. Macbeth's cure is to find an obsession - and so he does, with power and knowledge. It is after he loses his grip on reality at the dinner that he goes back in search of more prophecies. He is determined to know exactly how to keep the power he gained, in order to justify his own actions. He is mad with power, you might say. It is only just before his death that Macbeth realizes his own insanity.