How to calm down during a PANIC ATTACK! by psychcentral.
"Relax your breathing. Put one hand on your upper-chest, and the other over your diaphragm (where your rib cage meets your stomach).
Take in a slow, deep breath through your nose while counting to five. The hand on the chest should stay still, while the one over your diaphragm should raise with your breath. This is how you know the breath is deep enough.
When you reach the count of five, let the breath out slowly (through your nose) at the same rate. Concentrating on your hands and the counting will help focus you and calm you down. Continue these breaths until you feel relaxed.
Relax your muscles. Find a comfortable position to sit in (or lie down).
Close your eyes and begin to focus solely on your toes. Curl them under tightly for a count of five, squeezing the muscles together as hard as you can, then relax.
Next, concentrate on your feet. Contract all of their muscles tightly for a count of five, then relax.
Continue up your body, isolating each muscle group (calves, thighs, buttocks, stomach, chest, shoulders, neck, fingers, hands, and arms) all the way up to your face.
By the time you contract and relax your face muscles, you should feel much more calm."