Obstructive Sleep Apnoea (OSA)
The most common sleep disorder, obstructive sleep apnoea is characterised by repetitive upper airway narrowing or total collapse and is often associated with snoring, decreases in blood oxygen levels and sleep disruption ('micro-arousals'). There is a wide range of severity from occasional pauses in breathing to hundreds of times in a night and from a few seconds at a time up to minutes at a time of reduced or totally ceased breathing.

Many people are unaware of their obstructive sleep apnoea and report sleeping straight through the night but wake feeling 'hungover', however partners of people with sleep apnea will often notice them stopping breathing at night and find themselves counting how long they stop breathing for and waiting anxiously for them to start up again. Sometimes, partners of people with obstructive sleep apnoea will motivate them to consult their doctor because of the major disruption that snoring causes them.

Typical symptoms are waking un-refreshed, morning headaches, waking with a dry mouth, excessive daytime sleepiness (eg when doing relaxed or repetitive activities), difficulty concentrating or memory problems, mood changes such as irritability or depression, and decreased libido and/or impotence. The milder form can still be associated with snoring, sleep disruption and excessive daytime sleepiness. In its most severe form it is additionally associated with prolonged decreases in blood oxygen that can reach very severe levels with huge strain on the heart, brain and other organs.