One way that Macbeth has changed since Duncan's murder is that he has become much more paranoid. He fears people uncovering his murderous acts and begins to think that everyone around him must suspect him as a murder.
His behavior becomes more and more erratic, especially in Act Three, scene four, in which Macbeth startles to see Banquo's ghost sitting at the banquet table. When he sees the ghost, Macbeth is convinced that one of the lords must have placed it there to convict him of his murderous deeds. He questions the party-goers: "Which of you have done this?" and when the Lords have no idea what he is talking about, Macbeth adds:
"Thou canst not say I did it: never shake
Thy gory locks at me" (III.iv.60-64).
His over-whelming sense of guilt at Duncan's and then Banquo's murders have caused him to be completely paranoid and even hallucinatory. Macbeth's character changes for the worse after Duncan's murder; his guilt consumes him.