Breathwork is the deliberate manipulation of breathing pattern, depth, or rhythm to influence physiological state.
Mechanism: Slow nasal breathing (4-6 breaths/min) activates parasympathetic tone via the vagus nerve. Long exhales drop heart rate and blood pressure. Hyperventilation (Wim Hof, holotropic) shifts blood chemistry transiently.
Use case: 5 min of box breathing (4-4-4-4) for stress; 10 min of slow nasal breathing pre-sleep; physiological sigh (double inhale, long exhale) for acute stress relief.
Caveats: Don't combine intense breathwork with cold water plunging. Passing out is a real risk. Hyperventilation protocols not for pregnant women or unmedicated hypertension.