Depersonalization (or depersonalisation) can be referred as a malfunction or anomaly of the mechanism in which an individual has awareness or perception of his or her own self. It is a feeling of watching oneself act, while having no control over a situation. It can be considered desirable, such as in the use of recreational drugs, but it usually refers to the severe form found in anxiety and, in the most intense cases, panic attacks. A sufferer feels that he or she has changed and the world has become less real, 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".
Depersonalization is a subjective experience of unreality in one's sense of self, while derealization is unreality of the outside world. Although most authors currently regard depersonalization (self) and derealization (surroundings) as independent constructs, many do not want to separate derealization from depersonalization. The main reason for this is nosological, because these symptoms often co-occur, but there is another reason of great philosophical importance, namely, that the phenomenological experience of self, others, and world is one continuous whole. Thus, feelings of unreality may blend in and the person may puzzle over deciding whether it is the self or the world that feels unreal to them.