How has guilt changed Macbeth for the worse?

Macbeth experiences feelings of guilt almost immediately after killing Duncan. Even before the murder, he acknowledges that he has no good reason, other than "vaulting ambition," to kill the king. He tells his wife immediately after the assassination that he struggled to say "Amen," and that he thought he heard a voice cry "Macbeth shall sleep no more." Over time, Macbeth's guilt manifests itself in visions like these. After murdering Banquo, he thinks he sees his dead friend's ghost sitting in the spot at the banquet table he would have occupied. Beseeching the ghost not to "shake [his] gory locks at me," Macbeth is escorted from the room by his wife, who first blames the visions on fear, and then on a lack of sleep. Ironically, Lady Macbeth herself succumbs to her own sense of guilt in Act Five, when she is observed sleepwalking and trying to wash spectral blood from her hands. So essentially guilt weighs on the consciences of the two plotters, causing them to temporarily lose their sanity. The way that guilt acts on the psyches of the Macbeths is an important and fascinating theme in the play.