When stress hits, getting your breathing back to a normal rhythm is the fastest way of improving the situation.
Learn and follow these steps, this can be used as part of the STOPP Technique.
Take a deep, slow breath in through your nose for about
5 or 6 seconds (if deep breaths are a problem, do 5 shorter breaths in)
Hold for a few seconds
Breathe out slowly through your mouth for about 7
seconds (breathe out like you are whistling)
Repeat 10 times