Once Macbeth kills King Duncan, he hears the words "Sleep no more." That is exactly what happens to both of them. Because of their guilt, they are both insomniacs. They cannot sleep at night. In fact, in Act V, Scene 1, Lady Macbeth is observed sleepwalking. In that scene she reveals her secrets and the Gentlewoman and the Doctor overhear her words and feelings of guilt.
"Yet who would have thought the old man
to have had so much blood in him?"
While Lady Macbeth is slowly going crazy without sleep and the overwhelming feelings of guilt, Macbeth is becoming more and more paranoid. He wants to ensure that no one will be in his way. He immediately (after becoming king) hires murderers to kill Banquo, once his best friend, and also his son Fleance. To ensure that the murder occurs, he even hires a third murderer to join them--just to make sure the job gets done. Macbeth talks the first two men into hating Banquo so he knows that they'll go through with the killing.
After Banquo, he goes after Macduff's family. It's never ending.
Both Macbeth and Lady Macbeth can never really enjoy their royalty because of both the lack of sleep (guilt) and because of his paranoia.
The two malicious murderers are not happy in their ill-acquired positions for obvious reasons: they are overwrought with guilt and remorse and, therefore, cannot sleep. Macbeth has already received a portentous warning about what was to come soon after he assassinated King Duncan. We see Macbeth pronounce the following in Act ll, scene ll:
Methought I heard a voice cry 'Sleep no more!
Macbeth does murder sleep....'
Macbeth cannot enjoy his position because he is deprived of sleep after having committed his foul deed. He later, in Act lll, scene ll, tells Lady Macbeth:
But let the frame things disjoint, both the
Ere we will eat our meal in fear and sleep
In the affliction of these terrible dreams
That shake us nightly: better be with the dead,
Whom we, to gain our peace, have sent to peace,
Than on the torture of the mind to lie
In restless ecstasy.
It is obvious that Macbeth is suffering from insomnia. He states that his mind is tortured and that it would be better to be dead than suffer the sleepless agony brought on by his guilt.
In addition, he becomes paranoid and goes about having all those he believes are his enemies or a threat, such as Banquo, assassinated. He has Macduff's entire family and his servants executed. He is later tormented by Banquo's ghost. In Act lll, scene lV, his horror and his guilt are apparent when he addresses what he believes is Banquo's spirit at the banquet table:
Thou canst not say I did it: never shake
Thy gory locks at me.
In Act V, scene l, we discover that Lady Macbeth has been suffering the same perturbation experienced by her husband. Her gentlewoman informs the doctor that she has witnessed her walking in her sleep.
I have seen
her rise from her bed, throw her night-gown upon
her, unlock her closet, take forth paper, fold it,
write upon't, read it, afterwards seal it, and again
return to bed; yet all this while in a most fast sleep....
She furthermore mentions that Lady Macbeth has become afraid of the dark and that she consistently rubs her hands as if she is washing them. When Lady Macbeth later cries out, we learn exactly what it is that's troubling her.
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.
In the end she cannot live with the guilt anymore and commits suicide.
In scene lll, we discover that Macbeth has grown tired of his way of life and wishes for some relief:
I am sick at heart,
When I behold--Seyton, I say!--This push
Will cheer me ever, or disseat me now.
I have lived long enough: my way of life
Is fall'n into the sear, the yellow leaf;
And that which should accompany old age,
As honour, love, obedience, troops of friends,
I must not look to have; but, in their stead,
Curses, not loud but deep, mouth-honour, breath,
Which the poor heart would fain deny, and dare not.
The Macbeths have realized that their "overriding ambition" has not brought them the reward and fulfilment they thought it would. Throughout their reign they have been plagued by the results of their malice and have been living lives mostly overwhelmed by the torture and pain of their guilt.