Depersonalization disorder refers to Dissociative disorder in which feelings of Depersonalization are so severe they dominate the individual’s life and prevent normal functioning.
Other /More definition:
Depersonalization disorder refers to a syndrome marked by frequent episodes of feeling detached from one's own body and mental processes, as if one were an outside observer of oneself; symptoms must cause significant distress or interference with one's ability to function. It is a dissociative disorder in which the individual experiences recurrent and persistent episodes of Depersonalization which are so severe they dominate the individual’s life and prevent normal functioning.