A 23 year old single male was brought to Emergency exhausted and frightened. His father tells you that his son, who was previously healthy, had, for no apparent reason, a sudden attack of fear, dizziness, palpitations and the feeling that his heart

A 23 year old single male was brought to Emergency exhausted and frightened. His father tells you that his son, who was previously healthy, had, for no apparent reason, a sudden attack of fear, dizziness, sweating, palpitations and the feeling that his heart is going to stop beating. The symptoms started to decrease gradually after about 10 minutes. Which is the most likely diagnosis?