Disturbed sleep and associated daytime fatigue can have many adverse health consequences. Insomnia is not only a risk factor for certain mental conditions but a potential warning sign for serious mental or medical issues87.

Insomnia is a subjective condition, not least because ‘normal sleep’ patterns are difficult to define, varying greatly between people, and from night to night. So, whilst textbook definitions of insomnia differ slightly they are broadly consistent in describing the key features, notably: ‘difficulty in getting to sleep (sleep onset latency), difficulty staying asleep (sleep maintenance), early wakening, or non-restorative sleep despite adequate time and opportunity to sleep, resulting in impaired daytime functioning, such as poor concentration, mood disturbance, and daytime tiredness’3616397.

Traditionally, insomnia has been categorised as either primary (ie. no other conditions deemed to be responsible for the poor sleep) or secondary (ie. another disorder causally responsible for the poor sleep).

Primary insomnia: insomnia that occurs when no cause or comorbidity is identified. Commonly the person has conditioned or learned sleep difficulties with or without heightened arousal in bed. Typically primary insomnia has a duration of at least 1 month and accounts for about 15–20% of long-term insomnia61.
Secondary (or comorbid) insomnia: insomnia that occurs as a symptom of or is associated with other conditions including medical or psychiatric illness or drug or substance misuse61.

In practice however, determining the cause and effect of insomnia is often very difficult. Whilst these terms are still commonly used, in May 2013 the Diagnostic and Statistical Manual (DSM-5) of the American Psychiatric Association replaced the primary/secondary designation with a single term ‘insomnia disorder’. This change emphasises ‘insomnia disorder’ as a condition requiring independent clinical attention, regardless of other comorbid conditions or medical problems that may be present and also require treatment. So, a diagnosis of insomnia disorder is to be given when it is sufficiently severe, whether it occurs as an independent condition or is comorbid with another mental disorder, medical condition or another sleep disorder13.

Insomnia can be further described according to its duration – acute or short-term insomnia lasting less than 4 weeks, and long-term, persistent or chronic insomnia lasting for 4 weeks or longer.

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