My two pennies worth on the Emperor laughing, "No Want!!".

Palpatine isn't insane he is old and over confident (which explains why he acts like a bit of a git instead of being a calm and quiet sort of evil chap).

I can imagine him trying to figure out a way out of it all the way down to the bottom of the shaft (and failing because his time is finally up).

But he is certainly taken by surprise so his current response makes sense.

Making him laugh might be a set up for EU stuff like Dark Empire but I'm not comfortable with the EU slipping into the films (especially when we are suggesting many great ideas which move this film away from the EU).