Nasal breathing is breathing in and out through the nose, which slows and warms the breath and supports downshifting.
In 📝Breathwork the nose is the default for regulation. The mouth is available for a sigh, a release, or a more stimulating pattern when that is the aim. Nasal breathing is a method, not a diagnosis of mouth-breathing as a disease, and not a claim to treat apnea or sinuses. A stuffed nose is a reason to ease the demand, not to force the nostril.
Clients feel a slower, quieter cycle. If the nose is blocked, a softer mouth inhale with a nasal exhale is enough. Dizziness, panic, or chest pain is a stop.