Does Macbeth ever turn back to rational behaviour?
I think Macbeth's behaviour is all rational to begin with, as long as you step past the bit where he believes the prophecies of the witches (who, he knows and we know, can't really be trusted as rational guides in the first place).
He learns that he is to be king, and so kills the reigning monarch - and becomes king. Then, to prevent the next prophecy coming true (that Banquo's issue will be kings) he tries to kill Banquo and his heir too (he kills Banquo, but not Fleance). And lastly, to strip Macduff of heirs (and a claim to the throne) and also to punish him, he kills off Macduff's wife and family.
What's irrational is the appearing visions of Banquo's ghost, daggers which wave him toward Duncan and the witches' apparitions. But then again, is this Macbeth being irrational and mad? Is Banquo's ghost any less believable than the witches: and, after all, Banquo can see the witches perfectly clearly in the first scene. Perhaps it isn't simply in Macbeth's head.
In the end, Lady Macbeth turns irrational - mad. Macbeth, in that most painful of sanities, is profoundly aware of what he has done and what he has missed out on: love, troops of friends, honour... and so on. She goes mad. He stays painfully rational: even when, at the last, he decides he has no other option but to fight.