Why it caught on
Hyperventilation drops CO₂; breathing into a bag re-inhales exhaled CO₂ and quickly restores it, which can interrupt the panic loop within minutes.
Why it fell out of favour
Several documented cases of harm when chest pain or breathlessness was caused by a heart attack, pulmonary embolism, or asthma — not panic. Restricting oxygen in those situations is dangerous.
Modern guidance
Use slow breathing instead: long exhale, gentle nasal inhale, repeated for 90 seconds (see our rescue protocol). It is safer and works for the same reason.
When it might still be considered
Only under direct clinical supervision, when a clinician has confirmed the cause is hyperventilation.
Log your sessions in Breathe On and explore the matching guidance at [/breathing-for/panic-attacks](/breathing-for/panic-attacks).