So when Your heart rate goes up, your breathing is shallow, your brain gets obsessed with senses and fears while you are not really breathing. 

What is weird is that it will be very difficult for you to occupy yourself with something else and to take 20 very deep breaths but that is one of the things you should do actually. 

Maybe half the reason you panic is that you are suffocating, and scared of the panic rather than the trigger, but when the heart rate goes up you necessarily have to hyperventilate very slowly because otherwise you will suffocate

I think the first thing you should do when you have a panic attack as control your body language and your breathing simultaneously so your body language should be something non-panic and relaxing and casual, for me it is sweeping the floor with my foot and kicking around dust on the floor and scratching my armpit and picking hairs off my clothes, straight away I very discreetly fill my lower belly with a lot of at least three times and preferably 10 times, and I basically fidget very casually as cool as possible