Macbeth’s deteriorating mind in different way as a lots of things going through his mind and hes questioning him self that everything he did was useless because he had to kill his best friend to become king, and also  Macbeth was pushing him in a way that she though was right. now his wife lady Macbeth is dead

Macbeth is STRESSING over the death of his wife and is coming to the conclusion that there is no point in living. There is an army outside of his castle, and the thought of it is sending his mind into a frenzy.