A therapist on an inpatient unit conducts an intake with a 40-year-old man who was transported to the hospital by the police after an altercation in a park. He is unable to provide a medical or social history and reports having no memory before he arrived at the hospital. A police check reveals that he is an executive of a large company in a nearby city who was laid off a few days ago. At the end of his weeklong stay in the hospital, he has recovered his memory. The MOST likely diagnosis is...