Integrating what we see, hear, smell, taste, touch, feel, think, and do into a relatively unified experience is essential for our functioning. Integrating these different psychological, physiological, and behavioural aspects into a web of interacting memories, feelings, and actions fosters a more continuous sense of self (i.e., integration of the personality) and assists smooth and flexible interactions with the self, the environment, and other people. Dissociative disorders are characterised by a failure of this capacity. They are founded in dissociation, a disruption in the ability to bring together aspects of an experience or personality.
The Diagnostic and Statistical Manual of Mental Disorders (5th ed.; DSM-5; American Psychiatric Association, 2013) contains three discrete dissociative disorders: dissociative amnesia (DA); depersonalisation/derealisation disorder (DRD); and dissociative identity disorder (DID). There are also two broader categories with less discrete and specific criteria: other specific dissociative disorder (OSDD) and unspecified dissociative disorder (USDD). They are used when someone experiences debilitating symptoms that do not meet the previous discrete diagnoses. The core feature of DA (DSM-5 and ICD shared code F44.0) is the inability to recall information laid down in memory (i.e., encoded) about events one has experienced (e.g., autobiographical). This so-called reversible autobiographical memory loss is more serious and distressing than ordinary forgetfulness and is not caused by neurological injury or substance intoxication. The non-retrieved material is typically stressful in nature, such as the central details of being involved in a car accident where a loved one is killed. The person with DA typically has no problems learning new material or engaging in new or previously learned tasks. Amnesia may be localised, relating to a specific time period in the person's life in which they have little or selective memory (selective amnesia), or more rarely generalised, in which the person has a complete loss of memory for their life history. This total loss is experienced as one-half of the symptom profile for what is called dissociative fugue. Dissociative fugue is a subtype of DA. In addition to generalised amnesia for one's own identity (e.g., losing awareness of one's name, age, and history) it involves purposeful travel away from one's home or work, or wandering in a bewildered daze.