In Act 2, Scene 1, before Macbeth enters Duncan's chamber, he is already full of anxiety about killing Duncan. In this famous scene, he hallucinates and believes he sees a dagger. He is trying to put himself into a state of mind where he is capable of committing murder. Macbeth's soliloquy at the end of this scene consists of him talking himself into carrying out the murder. He experiences a lot of fear, anxiety, and potential guilt.
In Act 2, Scene 2, Macbeth tells his wife he has committed the murder. He also explains his state of mind as he went into Duncan's chamber. Macbeth claims that he heard Duncan's guards saying prayers. Macbeth reveals how guilty he felt and he adds that he couldn't say "Amen" upon overhearing their prayers. Lady Macbeth says he is overthinking things. He adds that he heard one of them say "Sleep no more! / Macbeth doth murder sleep-" / the innocent sleep." Macbeth was plagued by guilt and anxiety when he entered the chamber and those feelings continue and grow steadily worse after the murders have been committed.