It is funny that Hamlet drops the madness act for this scene. There are so many reasons to think that this scene and the speech that precedes it (at least in this version, see also the “bad quarto”) are both for show, that he’s doing them for the audience of Claudius and or Polonius, whomever he thinks might be spying.
And yet – this line leads rather clearly in the other direction. That is, if Hamlet is putting on the madness for the benefit of Polonius and/or Claudius, why does he drop it for this section? The only option would be that he doesn’t know they’re watching. Except. . .
Hamlet does some crazy stuff in this scene but it’s not so much like madness as the madness Ophelia describes to Polonius. It is not like madness – even if it does lack form a little.
Or, is Hamlet attempting to do his mad act and failing to convince Claudius? Possibly.