In this paper Reactive Dissociative Psychosis (RDP) is seen as a post-traumatic stress response and as a subcategory of Brief Reactive Psychosis (BRP). A review of the literature and the evolution of RDP from Hysteria and Hysterical Psychosis are given. Issue is taken with defining the duration of BRP as “Brief.” The authors argue that long-standing psychotic symptoms may be traumatically induced. The dissociative aspects of RDP as its key feature and the concomitant implications for accurate diagnosis are proposed. The usefulness of applying hypnosis in RDP treatment is summarized in a case study from Janet and detailed in a case from the authors' practice.