When it becomes disruptive in a person's life, it becomes a mental illness. These mental illnesses are known as dissociative disorders. These include dissociative fugue, depersonalization-derealization disorder (DPDR), and dissociative identity disorder. They can be triggered by trauma, stress, drugs, or no known reason. Sometimes other mental illnesses can involve dissociation. These include acute stress disorder, post-traumatic stress disorder (PTSD), and borderline personality disorder.