This breathing technique can help you to relax very quickly. It will work best if you have practiced it regularly when you don't need it.
1. Take a deep breath 2. Hold your breath for the count of three (counting under your breath) 3. Then let you breath out slowly, and as you let your breath out say to yourself the word R... E... L... A... X... 4. Breathe normally for 2 to 3 breaths 5. Repeat this four times
If you feel light headed breath more slowly.
Practice as many times each day as you can fit into your schedule, this way you will teach yourself to automatically remember the steps when you are feeling stressed.
You may find it useful to set the calendar in your phone to remind you to do this exercise a few times a day. If you do not have a phone maybe some little notes to yourself left in places where you will be reminded to complete the exercises.