What is the best thing to do to calm down when having a full blown panic attack?

When a person has a panic attack, their brain functions in the fight or flight responsive part of the nervous system;  this affects their impulse control, executive functioning, reasoning, and other brain activities related to safety. It is possible to recover from the physical symptoms of a panic attack.

The first thing the person will want to do is ensure they are in a safe place; that means if they are driving, pulling into a parking lot, or in a meeting excusing themselves, stepping out into the hall, taking a seat so they can focus on Mindfulness and Breathing. Dialectical Behavior Therapy (DBT) is an effective skills-based therapy for treating many mental health ailments, including panic attacks. One of the group categories is called distress tolerance. TIPP is one of the distress tolerance skills that are highly effective. 

TIPP stands for temperature, intense exercise, paced breathing, and progressive muscle relaxation. 

T - Temperature = changing your core body temperature, drinking ice water, taking a hot or cold shower (not too hot or cold so that you burn yourself), splashing cold water on your face, rubbing ice on the back of your neck. 

I- Intense exercise - speed walking, jogging, jumping jacks; the idea is to raise your heart rate and begin to produce endorphins. 

P- Paced Breathing. My favorite technique is starfish breathing because it focuses on slow-paced breaths, and you trace your hand, stimulating a tactile response.

P- Progressive Muscle Relaxation. There are a lot of techniques for Progressive muscle relaxation, but when at the moment, after your paced breathing, it has helped lots of people to do a small shoulder and/or neck role and shake their hands, shaking off the anxious energy. 

Sometimes people will only need to use one of these techniques to control a panic attack other times; they will need to utilize all four techniques to regulate their panic attack. Practice makes perfect. Having a plan helps reduce the fear of an impending panic attack. The more you utilize these skills before a panic attack, the more likely you are to use them during a panic attack. 

I hope this helps, and don't hesitate to contact a BetterHelp therapist if you have any questions or would like more support.