I've had to deal with panic attacks my whole life and most of the time I can link it up to an invisible stress meter building up until it triggers an attack. So

I've had to deal with panic attacks my whole life and most of the time I can link it up to an invisible stress meter building up until it triggers an attack. Sometimes I sort of mentally ignore how much stress I'm putting on myself due to work, life circumstances etc which doesn't make me realize how much stress I'm actually under until a panic attack finally hits. Breathing exercises and realizing that that I'm going through a panic attack usually helps defuse it a little though most of the time you can only just wait it out.