A 35-year-old man is in danger of losing his job because it requires frequent long-range traveling and for the past year he has avoided flying. Two years earlier he was on a particularly turbulent flight, and although he was not in any real danger, he was convinced that the pilot minimized the risk and that the plane almost crashed. He flew again 1 month later and, despite having a smooth flight, the anticipation of turbulence was do distressing that he experienced a panic attack during the flight; he has not flown since. What's the most appropriate diagnosis