Madness in the castle

The court of Denmark rots with madness as I speak - the Prince is deluded with hysteria; the King is dead, and 'tis ravaged with spying and secrecy. This night was not a good one.
Hamlet waited with Marcellus and me to find the ghost which we had found stalking the halls before. He did; he found him, and what followed was purely surreal.
The ghost beckoned him; he, who was behind the barrier of me and Marcellus. We feared to let him through. Surely, we did not want to lose the Prince. The loss of such a royal figure at our hands would create endless hindrance for us. But the Prince didn't agree. He was driven forth with the blurred (not quite blind, as it is understandable) urge to reunite with his father. And, so, he drew his royal sword and threatened us with it, pointing it's sharp and smooth edge in our faces. We let him through, forced by his utter powerfulness, and watched in despair as he ran to the ghost.
To have called this ghost "voiceless" was, in my hindsight, a grave mistake. His fervent, booming voice, bringing on our reminiscences while striking us with fear, preached to Hamlet for what seemed like years. It faded away and we scaled the castle, searching in pure terror for him.
When we finally found him, the ghost had vanished. Hamlet sat there. His countenance was different - much less plaintive, and much more uneasy and - dare I say - deranged.
And then he spoke, and I can say that I've never heard such a shocking change in character as how Hamlet spoke. After weeks of him only uttering low-register moans and mumbles of deathly melancholy, he was suddenly happy. But not in a satisfactory way -he seemed not satisfied at all. His happiness was almost mad - like he had finally been toppled over the edge, like the everlasting sadness had finally pushed him off the metaphorical cliff of sanity.
He spoke with such a queer gayness that it seemed completely out of place for such a dark time. We left that castle with a changed prince, a mentally blundered prince.
What has happened to Hamlet?