Well, God-a-mercy.
There’s something about this reply that leads Polonius to ask if Hamlet knows who he is. This leads me to wonder what Hamlet has said, or more probably neglected to say that makes Polonius wonder. Is it a simple breach of etiquette? What is the way that the prince usually addresses the king’s counselor, or Lord Chamberlin or whatever Polonius’ Official designation is? This particular response seems perfectly cordial. Hamlet’s been asked how he is. He says he is well and gives thanks for that to his god. Simple enough. Doesn’t seem to raise questions of identity or insanity or rudeness, even. Except it must because Polonius subsequently treats Hamlet like he’s 90 years old and losing his memory.
The Hamlet Project 