A 24-year-old woman presents after a brief loss of consciousness while standing on a crowded bus. Witnesses describe pallor, light-headedness, and gradual sagging to the floor. There is no incontinence, tongue biting, or tonic-clonic activity. She rapidly recovers and feels well. Examination, ECG, and orthostatic vitals are normal. Which feature would most strongly prompt hospital admission for further syncope evaluation?