Depersonalization is a type of dissociation disorder, yes. It's in the same class of disorder as multiple personalities - or Dissociative Identity Disorder.

And I think the discussions between Richard, Eliezer, and Robin, among others, are worth reading. Richard argues, in a nutshell, that the mind is more than just the brain, that there is something else that creates the mind. Eliezer and Robin argue that he his making the same mistakes that he has been describing in the Mysterious Answers to Mysterious Questions sequence. That's what the "zombie world" is all about - if a world consists of humans who are in every way exactly the same as ours minus whatever ephemeral thing it is that Richard says completes "consciousness", Richard argues these zombies will not be conscious, and Eliezer argues that they will be, because they are made of all the same things that we are.