What insomnia is: the diagnostic criteria

Why the definition matters

A great many people diagnose themselves with insomnia because they sleep less than eight hours, and a great many others do NOT think they have insomnia despite years of suffering, simply because they still get six. Both are using the wrong measure.

The international diagnostic criteria do not use hours, for two practical reasons. First, sleep need varies enormously between people. Second, people estimate their own sleep rather poorly, in both directions.

The four conditions

1. Night-time symptoms

At least one of three: trouble falling asleep, trouble staying asleep (waking in the night and struggling to get back), or waking earlier than intended and being unable to return to sleep. In children and in people who need a carer, the symptom may also be resisting bedtime or being unable to sleep without an adult present.

2. Daytime consequences

This is the condition that separates insomnia from natural short sleep, and it matters more than any of the others. At least one consequence has to be present: fatigue, poor concentration, reduced memory, worse performance at work or study, irritability, mood disturbance, daytime sleepiness, reduced motivation, more mistakes and accidents, or worry about sleep itself.

3. Frequency

Three nights a week or more. One restless night before an exam, or a few nights after a long flight, is not insomnia disorder.

4. Duration

Under three months is short-term insomnia; three months or more is chronic insomnia. The two differ in more than name: they differ in how they are approached.

The exclusion that gets forgotten

The criteria also require one more thing: the sleep problem must occur DESPITE having adequate opportunity and conditions to sleep. A mother with a small child who wakes at night, someone working two shifts back to back, someone sleeping in a room that is too noisy, are all sleep-deprived rather than suffering from insomnia disorder.

This distinction decides the approach. Lack of opportunity means the circumstances have to change; insomnia disorder means intervening in the mechanism keeping it going. Behavioural therapy for someone who simply does not have time to sleep will not help.

Primary insomnia and comorbid insomnia

The older classification divided insomnia into primary (a condition in its own right) and secondary (caused by something else). Current classifications have dropped that line, for a very practical reason: when someone has both depression and insomnia, arguing about which caused which does not help, whereas treating both does.

The practical consequence: if your insomnia accompanies another condition, it still deserves treatment in its own right rather than waiting for the other one to clear.

Three patterns of insomnia, and why they have to be told apart

The diagnostic criteria put all three night-time symptoms under one diagnosis, but in practice they lead to three different interventions. A good consultation always asks carefully which pattern you have, because the answer decides most of the plan.

Insomnia with non-restorative sleep

There is a group that fits none of the three patterns above: they sleep enough hours, do not wake much, and still get up feeling as though they never slept. The sensation is very real and very unpleasant, but on its own it is NOT enough to diagnose insomnia disorder.

The reason is that this symptom group points strongly towards other conditions: sleep apnoea shatters sleep without the person remembering waking; restless legs syndrome and periodic limb movement disorder do the same; depression, hypothyroidism, anaemia and several chronic conditions all produce a similar feeling. That is why the "slept enough and still wrecked" pattern needs assessment rather than self-management.

Insomnia in particular groups

• Older adults. A slightly shorter and lighter sleep is a normal physiological change, not an illness. It becomes a problem when the person keeps their old bedtime and spends too long in bed.
• Women in the perimenopausal years. Hot flushes and night sweats are a clear physical cause needing their own management, not only behavioural intervention.
• Night-shift workers. This is usually a circadian rhythm disorder rather than insomnia, and the approach is quite different.
• Children. The symptoms present differently: resisting bedtime, being unable to sleep without an adult. This needs a paediatric specialist.