A 40-year-old woman with ...

A 40-year-old woman has been experiencing sudden episodes of palpitations, sweating, trembling, shortness of breath, chest pain, dizziness, and feeling as if she is going to die for the past four months. The first episode occurred without any apparent reason and lasted about 15 minutes. Since then, she has had similar episodes 1-2 times a day, unexpectedly, in different situations. She worries almost constantly about when she will have another attack and is convinced that she is having a heart attack. All physical and laboratory examinations have yielded normal results, and she denies drug use. She is being treated for hypothyroidism with levothyroxine. What will be the diagnosis? Suggest further management.