Obstructive Sleep Apnoea
Loss of upper airway muscle tone during sleep allows soft tissue (worsened by obesity and anatomical crowding) to collapse the pharynx, causing repeated episodes of partial or complete airway obstruction that fragment sleep and cause intermittent hypoxia, so the daytime and cardiovascular consequences all trace back to sleep that is never allowed to become restorative.
First principles
The airway collapses because muscle tone, not structure alone, keeps it open
Unlike the trachea, the pharynx has no rigid cartilaginous support: it is held open during wakefulness by tonic activity of the pharyngeal dilator muscles (including genioglossus). During sleep, this muscle tone physiologically falls. In most people the airway remains adequately patent, but where the airway is already narrowed, by obesity (fat deposition around the neck and pharynx), enlarged tonsils, retrognathia or other anatomical crowding, this normal sleep-related relaxation is enough to let the soft tissues collapse inward and obstruct airflow, either partially (causing snoring as air vibrates through a narrowed passage) or completely (apnoea).
Educational content pending clinical review. Not medical advice.