When you are stressed out, sometimes all it might take to get grip on the situation again is to halt yourself, and take a few, deep breaths.
Even though I wrote about breathing exercises previously, I did not touch upon how to breathe exactly for this purpose.
To calm your body's reaction to stress, you can use diaphragmatic breathing. I could describe it, but the video below shows you in 2 minutes how to find your deep breathing for yourself.
Do take 2 minutes to get the basic idea of breathing with your diaphragm: