Is Macbeth Crazy in Act 2 Scene 1?

Macbeth met three witches who made two prophecies, the first came true, the second promises Macbeth's death. One put into that scenario might begin to question their own sanity and their mind would be put into a strange uncomfortable place.

The dagger in the soliloquy is a window into Macbeth's brain. He still tries to remain rational but his way of thinking isn't quite right. He knows there is no physical dagger present, but the metaphor with the dagger is a way to describe what he is thinking.