Yoga, meditation and tantric breathing techniques have helped me a LOT. And it's true; it very much helps to realize that whenever your mind is going in circles and your heart's racing, it's not that something's actually wrong - it's just your nervous system jumping the gun for no reason and having hard time to exit the 'fight or flight' stage.
Also, something that works for dogs and humans alike; since the symphatetic nervous system effectively shuts down all digestion, eating calms you down, because it forces the parasymphatetic system to activate and work as a balancing force. That's why when I'm having an attack, I eat less and less, and sadly also why so many people are addicted to 'comfort eating'. But maybe having a banana or an apple to munch on might offer a quick relief?
Me: bi female in my twenties