Bert is standing in a shopping mall when he begins having difficulty breathing. He feels his heart pounding, feels weak and dizzy, and notices that he is perspiring heavily. He feels like he might be having a heart attack. At the very least, he senses he is losing control and is afraid that if he's not having a heart attack, he is going "crazy." Assuming that Bert is not having an actual heart attack, he is most likely suffering from ______.
