The hallucinations seen by Macbeth and Lady Macbeth throughout Shakespeare's tragedy are symbolic of the duo's guilt for engaging in bloodshed to further their personal ambitions, according to SparkNotes. The first hallucination is the floating dagger Macbeth sees right before he kills Duncan. Lady Macbeth's famously hallucinates blood on her hands that cannot be washed away.
The characters see these visions as supernatural signs of their guilt as the action progresses. Shakespeare leaves it up to interpretation as to whether or not these hallucinations are real or simply imagined concepts within the minds of the Macbeths.
These ephemeral visions also signify Macbeth's war within himself as his honor battles ambition, according to LitCharts. When Macbeth hears a voice saying "does murder sleep," it foretells Lady Macbeth's sleepwalking and Macbeth's nightmares about murdering his friends.
Blood, both real and imagined, symbolizes the guilt on the hands of the Macbeths. In the beginning of the play, the Scots ward off Norwegians in a real battle with many casualties. After imagining a bloody dagger upon Duncan's death, Macbeth wonders if "great Neptune's ocean" is enough to wash away what he does. By the end of the play, Lady Macbeth imagines blood on her hands by saying "out damned spot." Hallucinating blood in her sleep, Lady Macbeth's psyche tries to wash away her guilt to no avail.