Ronny was once stranded in an elevator all by himself because of a power outage. It was nearly 10 hours before a rescue team came and got him out of the elevator. After this incident, Ronny had a panic attack whenever he got into an elevator. Several months later, the attacks stopped and Ronny could comfortably get into elevators. Then, one day, he had an unexpected panic attack again as he got into an elevator in his office building. This scenario exemplifies ________.