We know what Macbeth and Lady Macbeth *do*; what they feel may be up for interpretation depending on how we read what they do and say. For instance, we know that Macbeth murders the guards as they are starting to wake from their drugged state, and says that he's done it out of his love for the king (who could refrain, that had a heart to love, and in that love, courage to make his love known). We also hear Macbeth say "I do repent me of my fury" in explanation for his apparently rash act of killing the guards. But what does he feel? Guilt, definitely, but also borderline panic. His "fury" was probably fear that the guards would start to speak, and cast reasonable doubt on whether or not they were actually guilty of the crime the Macbeths were trying to frame them for. We also know Lady Macbeth faints just as Macbeth is in the midst of rationalizing his actions. Has she fainted because she has had a long night? Some say so, and further suggest that this marks the beginning of the Lady's weakness. It is possible that the night has been too much for her--she probably hasn't eaten, and she certainly hasn't slept; however, the timing of her fainting spell is simply too perfect, especially given that before she faints she draws attention to herself saying, "Help me hence, ho!" Were this a genuine fainting spell, she would be incapable of such a long utterance. So my reading of her action would be that she's seen her husband on the verge of bumbling the whole thing and she takes a dive--so to speak--to take the focus away from him. If this is the case, then at this point in the play she is still the one in control: he acts on impulse while she calculates their moves.