In the Cast Commentary, Elijah Wood describes the scene as "a little bit Dorothy waking up, being in Oz..." and it seems at least to me that Elijah has some doubts about the scene, but PJ reassures him that all will be well - need I say more?
Orlando Bloom states that Merry and Pippin's entrance and demeanor were "perfect."
Elijah calls it the "laughter scene," and adds more about how much everyone was laughing. Sean Astin describes it as "angelic and beautiful." When Merry dives on the bed, Dominic Monaghan says that he didn't know what he was doing there, "but Pete obviously must have liked it."
Peter Jackson states that it would be a difficult scene, and that he asked Ian's (McKellan) advice, which was for everyone to laugh. Philippa Boyens says that "some people hate this stuff" and so she must have received my letter
.
The Production team states that these scenes are "coda," and that the movie really ended with Frodo in the Eagle's clutches. There seems to have been the choice of all smiles or laughter, and we see which the team chose. Gandalf and the hobbits are actually in the scene together, and the other "heroes" are digitally stitched in, which may explain why they react differently, not seeing what's going on. Someone from this team states that the scene was originally longer, with the action in even more slow-motion, but the scene was sped up as it was deemed pretty much unnecessary. The point from this team's point of view that the thought was to reunite Frodo with Gandalf, and the rest was 'extra.'
Just thought you might want to know.