A 32-year-old woman from Delhi presents to the psychiatry outpatient department with a 2-year history of sudden, unpredictable episodes of intense fear lasting 10–20 minutes. During these episodes, she experiences palpitations, diaphoresis, trembling, dyspnea, chest discomfort, and a fear of dying or losing control. Between episodes, she worries constantly about having another attack and has begun avoiding crowded places, public transport, and shopping malls. She denies any medical illness, substance use, or recent stressors. Physical examination and baseline investigations are unremarkable. What is the most likely diagnosis?