What is the nasal cycle?

The nasal cycle is a physiological phenomenon where airflow through your nostrils alternates in dominance. Every two and a half hours, on average, the airflow in one nostril becomes more dominant while the other becomes less so. This alternation is especially pronounced during sleep. The nasal cycle reflects changes in the autonomic nervous system, specifically the balance between the sympathetic and parasympathetic components. The balance in this system affects the shift from left to right nostril and is essential for various physiological functions 1.