"Depersonalization is a concept difficult to delineate. It can be regarded as a symptom or as a loosely associated group of symptoms that occurs in psychiatric patients. It can be induced experimentally and also occurs spontaneously in normal subjects. A major obstacle to clearer definition of this concept lies in the fact that it refers to exceedingly private events in the individual's experience. These prove very difficult to describe by a language geared to the description of public (consensually validated) events or private events, such as pain, that occur usually in clearly defined social settings. When it comes to describing and conveying something as ineffable as depersonalization or derealization, the subject resorts to metaphors, "as if" expressions, and figures of speech. The result is semantic confusion. Different authors mean different things when they use the term depersonalization. The concept of depersonalization merges by imperceptible degrees with the concept derealization, the concept of altered body image and self, deja vu, jamais vu, altered time and space perception and so on - the whole gamut of phenomenological description of the experiences of mental patients. Therefore, it is rather difficult to evaluate and to review objectively the psychiatric literature on the phenomena of depersonalization."