In act 5, scene 3, the Doctor has a short scene with Macbeth, who orders the Doctor to cure Lady Macbeth of what the Doctor terms...
The only comic aside that appears in Shakespeare's Macbeth belongs to the Doctor who observes Lady Macbeth's sleepwalking in act 5, scene 1.
In act 5, scene 3, the Doctor has a short scene with Macbeth, who orders the Doctor to cure Lady Macbeth of what the Doctor terms "thick-coming fancies," meaning her disturbing dreams, and what Macbeth believes is her "diseased mind."
Macbeth then tells the Doctor,
I will not be afraid of death and bane,
Till Birnam forest come to Dunsinane (5.3.68-68).
The Doctor remarks, in an aside:
DOCTOR: Were I from Dunsinane away and clear,
Profit again should hardly draw me here. (5.3.70-71)
In other words, the Doctor is saying that if he ever gets away from the castle at Dunsinane, Macbeth couldn't pay him enough to come back again.
One of the most famous scenes of comic relief in a Shakespeare tragedy is what is referred to as the "Porter scene" in Macbeth. The scene occurs in act 2, scene 3, immediately after Duncan's murder by Macbeth and Lady Macbeth. The "Porter scene" also serves as a prelude to the scene when Duncan's body is discovered by Macduff.
Macbeth's porter is roused from his drunken stupor by loud knocking at the castle gates. He goes to open the gates, and on his way he gives a comic soliloquy comparing the gates of the castle to the gates of hell.
PORTER. Knock, knock, knock, knock! Who's there, i’ the name of Beelzebub? ... Knock, knock! Who's there, in th’ other devil's name? ... But this place is too cold for hell. I'll devil-porter it no further. (3.2.3-4, 7, 15-16)
Low comedy ensues when the Porter finally opens the gates and admits Macduff, who comes to meet with Duncan. There is a short dialogue between the Porter and Macduff, in which the Porter tells Macduff that drinking "is a great provoker of three things" (3.2.23).
MACDUFF. What three things does drink especially provoke?
PORTER. Marry, sir, nose-painting, sleep, and urine. Lechery, sir, it provokes and unprovokes: it provokes the
desire, but it takes away the performance. (3.2.24-27).
In this same scene there are examples of droll, high comedy and irony which juxtapose the audience's knowledge of the murder of Duncan with the questions and remarks made by Macduff, Lennox, and Macbeth.
MACDUFF. Is the King stirring, worthy Thane?
MACBETH. Not yet. (3.2.42-43) ...
LENNOX. Goes the King hence today?
MACBETH. He does: he did appoint so. (3.2.53-54)
Lennox tells Macbeth about the unusual events that occurred during the night.
LENNOX. The night has been unruly. Where we lay,
Our chimneys were blown down, and, as they say,
Lamentings heard i’ the air, strange screams of death,
And prophesying with accents terrible
Of dire combustion and confused events
New hatch'd to the woeful time. The obscure bird
Clamor'd the livelong night. Some say the earth
Was feverous and did shake. (3.2.55-62)
Macbeth's masterfully understated response summarizes not only Lennox's description of what occurred during the night, but also summarizes Macbeth's state of mind and Macbeth's reaction to what he experienced during the night.
MACBETH. ’Twas a rough night. (3.2.63)