Cautions apply
This is one of the two places in the book with a skip list. Read the chapter in full before you use it, and read Before you begin. Seated, never near water, never in a moving car. Anyone with a panic disorder, a strong history of panic attacks, or CO2 hypersensitivity skips every held breath in the book.
The short version
A brisk, forceful, rhythmic breath through the nose, belly pumping, roughly 1–2 per second, for about 30 seconds, not five minutes; more is not better. Then stop, let go completely, and sit still and notice, because the release afterward is the technique, not the pumping. Sit down every time. Has real contraindications (pregnancy, cardiovascular conditions, high or low blood pressure, a history of stroke, a respiratory condition such as asthma or COPD, epilepsy, glaucoma, panic history, recent surgery) and must never be combined with being in or near water, or done standing. Read chapter 7 in full before using this one.
What the research says
What the pumping does is blow off carbon dioxide and, with the effort, wake the adrenaline system for a moment; it does not load you with oxygen, because your blood is already close to saturated. Hyperventilation-style practices report more adverse events than slow ones in the one safety analysis that looked. Cited under Chapters 7 and 13.
Rooms where it does the work
Two rules, no exceptions
Never practice any technique on this site while you are driving, operating machinery, or doing anything that needs your full attention. The slow ones can make you drowsy, faster than you’d expect. And never practice a breath-hold, bellows breath, or any vigorous breathing in or near water. Read Before you begin for the doctor’s list and the rest.
The short version is a reminder, not a lesson. The chapter has the story, the steps, the mistakes, and the limits.