A 42-year-old woman from Mumbai presents with a 6-month history of recurrent episodes of palpitations, chest tightness, and a sensation of impending doom. During an episode in the clinic, she is noted to have a heart rate of 110/min, blood pressure 155/95 mmHg, and visible trembling. Her pupils are dilated. Interestingly, she reports that her symptoms are triggered by emotional stress and crowded places, and she has no cardiac pathology on investigation. A diagnosis of panic disorder is made. Which autonomic mechanism is primarily dysregulated in this patient's condition?