I've only had a 'true' panic attack once. I was running for a train and I slipped on the stairs and landed hard on my back. My throat closed up, my back ached and I couldn't shout, or call for help. Suddenly I couldn't breathe at all. I didn't know it was panic; I thought maybe I'd broken my back or something. Which of course made the panic worse.

I remember thinking "This is it. This is how I die, here on the station platform, alone, with nobody noticing." It was a terrifying, helpless feeling. It passed after maybe 30 seconds, as soon as I managed to take a gasp of air.

It was only once and more than a decade ago but even typing this is kind of freaking me out.