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EC: The Wim Hof breathing technique is as follows:
Sitting in a comfortable place, take 30-40 quick, deep breaths, inhaling through your nose and exhaling through your mouth. Then, take a deep breath and exhale; hold until you need to breathe in. Inhale again, as deep as you can, and hold it for 10 seconds. Repeat as many times as you like.
More details here: https://www.wimhofmethod.com/breathing-exercises