The Wim Hof breathing is a very intens breathing technique that will allow me to control the autonomous systems of my body and relieve stress. I tried this one before as a preparation an Ice Bath. Check the video if you haven't done so yet.
This technique is so interesting and allows you to go harmless into extreme situations. Wim Hof, is holder of 20 Guinness World Records for withstanding extreme temperatures. He has climbed Everest and Kilimanjaro with minimum clothing; he comfortably stays in ice baths for hours, and runs a full marathon in the highest desert (50 degrees celsius, 122 Fahrenheit) with no water & food. He uses this breathing technique to stay in control of his body & mind.