Can any doc tell me what's the difference between derealizatuon and depersonalisation?

Detachment: is common to both conditions. In the former, one feels that he is an outside observer of his surroundings--things look unreal, foggy, dreamlike. In the latter the observer feels the same way, only the focus is on his own internal experiences like mental processes, feelings/thoughts, imagery, physical numbing. etc. These two are a bit confusing...

Self vs. Environment: Depersonalization is feeling as though you are detached from yourself. Derealization is feeling detached from one’s sense of his or her surroundings