Apnoea is a breathing pause of at least 10 second.
Hypoapnoea is a 10 second event where there is continuous breathing but ventilation is reduced by at least 50 % from the previous baseline during sleep.

Sleep apnoea is the most common cause of excessive day time sleepiness. Sleep apnoea or apnea is a disorder characterized by a reduction or cessation (pause of breathing, airflow) during sleep. It is common among adults but rare among children. There are two types of sleep apnea, obstructive sleep apnoea and the central sleep apnoea. Most Common of the two is obstructive sleep apnoea also called Obstructive Sleep Apnoea/ Hypoapnoea syndrome (OSAHS).

When there is no airflow but there is effort to breathe, the apnea is called “Obstructive”. When there is no airflow but no respiratory effort the apnea is called “Central”. Mixed apneas start with no effort but effort develops during the course of the apnea.