A 29-year-old woman presents with a history of recurrent depressive episodes and intermittent periods of elevated mood, increased energy, and decreased need for sleep lasting 5-6 days at a time. She reports chronic feelings of emptiness, a pattern of unstable relationships, and frequent impulsive spending. Her family history is significant for bipolar disorder in her mother. She denies any self-harm behaviors but acknowledges that her mood shifts sometimes occur after interpersonal conflicts. Which of the following assessment findings would most strongly support a diagnosis of bipolar II disorder over borderline personality disorder in this patient?