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
Not a technique, but the understanding that the urge to breathe tracks carbon dioxide, not a true shortage of oxygen, which takes some of the fear out of a held breath at the end of a phrase, under a bar, or in an MRI tube. The only open-ended pause the book asks for stops at the first urge, seated, never near water, never in a moving car. Never load up on big breaths before any hold. Hyperventilating into a hold, especially in or near water, is the combination that has killed people. Anyone with a panic disorder, a strong history of panic attacks, or CO2 hypersensitivity skips every held breath in this book, including box breathing’s corners and 4-7-8’s hold; the plain in-and-out versions are given alongside each.
What the research says
Standard respiratory physiology. People with panic disorder show measurably greater reactivity to rising CO2, which is why the book asks them to skip every held breath. Hyperventilating before a hold, especially in or near water, is the combination that has killed people. Cited under Chapter 8.
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.