A 17-year-old Japanese girl experienced complete amnesia and dissociative symptoms following her mother’s depressive relapse and hospitalization. The patient had a history of domestic violence and had taken on a caregiving role for her mother. Three weeks before seeking help, she developed episodic stupor, involuntary eye deviation, and transient unconsciousness, along with generalized amnesia affecting various memory types. Neurological and medical evaluations ruled out physical causes, prompting a psychiatric referral. Over time, she began to remember witnessing her mother’s suicide attempt two years earlier, leading to a diagnosis of dissociative amnesia, dissociative stupor, and conversion disorder. These symptoms were attributed to psychological distress. Treatment included supportive psychotherapy, psychoeducation, and environmental stabilization, resulting in symptom resolution without medication. This case illustrates the complexities of diagnosing dissociative disorders, especially when trauma-related memory loss obscures the underlying stressor. It emphasizes the need for thorough psychological assessment and careful exclusion of organic causes in similar cases.