Psychiatrists, what is the difference between derealization and depersonalization?

Different: These are kind of close, yet definitely not the same. Depersonalization is the sense that one is detached or disconnected from his/her own experience -- so that one's self, body, and mind seem alien. Derealization is a change in the person's experience of the environment -- making the world around him/her seem strange, unfamiliar, or unreal. Both can come with several different conditions, also.