Like blood, hallucinations represent the guilt Macbeth and Lady Macbeth feel for having committed the mortal sin of regicide
The hallucinations include:
The bloody dagger (seen by Macbeth, Act I, Scene VII)
The voice stating that Macbeth has murdered sleep (Macbeth, Act II, Scene II)
Banquo’s ghost (Macbeth, Act III, Scene IV)
Blood on hands (Lady Macbeth, Act V, Scene I)
Only Lady Macbeth and Macbeth hallucinate in the play, and only they can see their own hallucinations:
Shakespeare may be suggesting that these are not, in fact, real visions, but exist only in the minds of our main characters
They could, therefore, represent the characters’ psychological realities