Excessive day time sleepiness is a disturbing symptom caused by number of diseases. Of them most common is sleep apnoea. 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).

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.