Depersonalization (or epersonalisation) is an 'alteration' in the perception or experience of the self so that one feels 'detached' from, and as if one is an 'outside' observer of, one's mental processes or body. 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 case, 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."