Table 2.

Sleep disorders and their symptoms.

Sleep disorder/symptom	Definition/key symptoms	Population prevalence (from DSM-V APA, 2013)
Insomnia	Difficulty initiating or maintaining sleep or nonrestorative sleep causing significant functional impairment.	6–10%
Sleep apnoea	A breathing related sleep disorder where breathing is obstructed during sleep, blocking off airflow and disturbing sleep. The primary symptoms are loud snoring and daytime sleepiness.	2–4%
Hypersomnia	Characterised by symptoms of excessive daytime sleepiness, and/or extended nocturnal sleep period.	1%
Parasomnias	A group of sleep disorders linked by abnormal behaviours, emotions, and dreams during sleep that lead to intermittent awakenings and difficulty resuming sleep.	Varies across disorder
Nightmare disorder	A disorder within the parasomnia group, characterised by frequent nightmares causing clinically significant distress or impairment in functioning — one or more episodes a week is classed as moderate severity.	6%
Circadian rhythm sleep–wake disorders	A group of sleep disorders resulting primarily from alteration of the circadian system or to misalignment between the endogenous circadian rhythm and the sleep-wake schedule required by an individual's environment. These disorders are split into types by the alteration seen for example — delayed sleep phase, advanced sleep phase and non-24 h sleep-wake type.	Varies across sub-type