Depersonalization (or derealization) is the feeling that 'nothing is real'; there is no or little sense of reality. It can be desirable, such as in the use of recreational drugs, but it is usually referring to the severe form found in anxiety and in the most intense case, panic attacks. It is most often described as a symptom of emotions, such as panic or fear. A sufferer feels that he or she has changed and the world has become less real ā?? it is vague, dreamlike, or lacking in significance. It can sometimes be a rather disturbing experience, since many feel that indeed, they are living in a "dream." The DSM-IV categorizes depersonalization disorder as a dissociative disorder, though depersonalization proper is more often characteristic of the traumatic origin of other conditions.

This might help.