Macbeth dismisses all reports about Malcolm's army, saying he'll fear nothing until Birnam Wood marches to Dunsinane and mocking Malcolm as a man born of woman. He shouts for his servant Seyton to bring his armor, then muses how sick at heart he feels, how withered his life has become.
Macbeth is fearless because of the prophecies, but he seems to wish he weren't. He knows his life is awful, but he's so gripped by ambition that he can't turn back.
He asks the doctor about Lady Macbeth, then commands that the man cure her. In an aside, the doctor says that if he could escape Dunsinane, no fee of any size could bring him back.
Macbeth seems totally out of touch with reality. He is a man warped beyond any semblance of humanity.