|Classification and external resources|
A fugue state, formally Dissociative Fugue (previously called Psychogenic Fugue) (DSM-IV Dissociative Disorders 300.13), is a rare psychiatric disorder characterized by reversible amnesia for personal identity, including the memories, personality and other identifying characteristics of individuality. The state is usually short-lived (hours to days), but can last months or longer. Dissociative fugue usually involves unplanned travel or wandering, and is sometimes accompanied by the establishment of a new identity. After recovery from fugue, previous memories usually return intact, however there is complete amnesia for the fugue episode. Additionally, an episode is not characterized as a fugue if it can be related to the ingestion of psychotropic substances, to physical trauma, to a general medical condition, or to psychiatric conditions such as delerium, dementia, bipolar disorder or depression. Fugues are usually precipitated by a stressful episode, and upon recovery there may be amnesia for the original stressor (Dissociative Amnesia).
The etiology of the fugue state is related to Dissociative Amnesia, (DSM-IV Codes 300.12) which has several other subtypes: Selective Amnesia, Generalised Amnesia, Continuous Amnesia, Systematised Amnesia, in addition to the subtype Dissociative Fugue.
Unlike retrograde amnesia (which is popularly referred to simply as "amnesia", the state where someone completely forgets who they are), Dissociative Amnesia is not due to the direct physiological effects of a substance (e.g., a drug of abuse, a medication, DSM-IV Codes 291.1 & 292.83) or a neurological or other general medical condition (e.g., Amnestic Disorder due to a head trauma, DSM-IV Codes 294.0). It is a complex neuropsychological process.
As the person experiencing a Dissociative Fugue may have recently suffered the reappearance of an event or person representing an earlier life trauma, the emergence of an armoring or defensive personality seems to be for some, a logical apprehension of the situation.
Therefore, the terminology fugue state may carry a slight linguistic distinction from Dissociative Fugue, the former implying a greater degree of motion. For the purposes of this article then, a fugue state would occur while one is acting out a Dissociative Fugue.
A doctor may suspect dissociative fugue when people seem confused about their identity or are puzzled about their past or when confrontations challenge their new identity or absence of one. The doctor carefully reviews symptoms and does a physical examination to exclude physical disorders that may contribute to or cause memory loss. A psychologic examination is also done. Sometimes dissociative fugue cannot be diagnosed until people abruptly return to their pre-fugue identity and are distressed to find themselves in unfamiliar circumstances. The diagnosis is usually made retroactively when a doctor reviews the history and collects information that documents the circumstances before people left home, the travel itself, and the establishment of an alternate life.
Agatha Christie disappeared on 3 December 1926 only to reappear eleven days later in a hotel in Harrogate, apparently with no memory of the events which happened during that time span.
Jody Roberts, a reporter for the Tacoma News Tribune, went missing in 1985, only to be found 12 years later in Sitka, Alaska, living under the name of "Jane Dee Williams." While there were some initial suspicions that she had been faking amnesia, some experts have come to believe that she genuinely suffered a protracted fugue state. 
David Fitzpatrick, a sufferer of dissociative fugue disorder from the United Kingdom, was profiled on Five's television series Extraordinary People. He entered a fugue state on December 22, 2005, and is still working on regaining his entire life's memories. 
Hannah Upp, a teacher from New York, went missing on August 28, 2008. She was rescued from the New York Harbor on September 16 with no recollection of the time in between. The episode was diagnosed as dissociative fugue.