Act 2, Sc. 2, lines 1-18: Why might the King be worried about Hamlet's behavior?

King. Welcome, dear Rosencrantz and Guildenstern!

Moreover that we much did long to see you,

The need we have to use you did provoke

Our hasty sending. Something have you heard

Of Hamlet's transformation - so I call it,

Since nore th'exterior nor the inward man

Resembles that it was. What it should be,

More than his father's death, that thus hath put him

So much from th'understanding of himself

I cannot dream of. I entreat you both

That, being of so young days brought up with him,

That you vouchsafe your rest here in our court

Some little time, so by your companies

To draw him on to pleasures and to gather,

So much as from occasion you may glean,

Whether aught to us unknown afflicts him thus

That, opened, lies within our remedy.