Waking in the night is the norm. Struggling to get back to sleep is not.

Waking up during the night is one of the most common experiences in adult life: 35.5% of a representative American sample reported waking at least three nights a week, and 31.2% of a five-country European sample reported the same [s1] [s2]. The variable that separates ordinary night-waking from a problem is not how often it happens but whether the person can get back to sleep — and only 7.7% of the European sample could not [s2].

That second number carries almost all of the harm, and it is the one worth knowing.

How common, and for how long

The American figures come from telephone interviews with 8,937 non-institutionalised adults aged 18 and over in Texas, New York and California [s1]. Within the 35.5% who woke at least three nights a week, 23% of the whole sample woke at least once every night, 4.5% woke five or six nights a week, and 7.9% woke three or four nights a week [s1]. More than 90% of those affected said the problem had lasted longer than six months [s1].

The European survey covered 22,740 non-institutionalised people aged 15 and over in France, the United Kingdom, Germany, Italy and Spain [s2]. Of the 31.2% (95% CI 30.6–31.8%) waking at least three nights a week, 7.7% (95% CI 7.4–8.0%) reported difficulty resuming sleep afterwards [s2]. In 78.8% of cases the symptom had lasted longer than a year [s2].

So night-waking is not a marginal experience, and it is not usually a passing one either. About 40% of the Americans with nocturnal awakenings also reported other insomnia symptoms — which means the majority did not [s1].

Why difficulty resuming sleep is the variable that matters

The European study measured daytime consequences and found them concentrated in one group. Difficulty resuming sleep had a greater impact on daytime functioning than any other pattern of nocturnal awakening, and than other insomnia symptoms, with odds ratios five to seven times higher than for people who simply woke once or twice within the same night [s2]. The relationship was dose-responsive: odds ratios rose with the number of awakenings in a night and with the difficulty of getting back to sleep [s2].

The company that difficulty resuming sleep keeps is also informative. People with a painful physical condition or a psychiatric disorder were more than four times as likely to have it [s2]. Other factors significantly associated with nocturnal awakening in that survey were hypertension, cardiovascular disease, upper airway disease, diabetes and heavy caffeine consumption [s2]. The American survey found a broadly similar pattern: organic diseases and psychiatric disorders were more frequent among people waking at least three nights a week, and nightly awakenings in particular were associated with more frequent organic disease, obesity and psychiatric disorders [s1].

What neither survey can tell you

Neither study identifies an hour. Both characterised awakenings by frequency per week and per night, by duration, and by the reasons people gave for them [s1] [s2]. Nothing in either dataset singles out a particular point in the night, and the popular fixation on a specific clock time has no support in this epidemiology one way or the other.

They are also both cross-sectional telephone surveys of self-reported sleep, conducted more than a decade ago. They establish how widespread the symptom is and what it travels with. They cannot establish what causes it in a given person.

The study that asked what actually woke people

For that, there is a small and uncomfortable piece of work. Twenty adults with chronic insomnia, enrolled between April 2008 and February 2010 at a community sleep centre, had never seen a sleep specialist, had never had sleep testing, and reported none of the classic symptoms of sleep-disordered breathing [s3]. Each gave a qualitative interview about why they thought they were waking, and each then had a diagnostic sleep study [s3].

Their own explanations were: uncertain cause (50%), nightmares (45%), nocturia (35%), bedroom distractions (20%) and pain (15%) [s3]. No patient identified breathing symptoms as a cause [s3].

The sleep studies recorded 531 awakenings across the sample. Of those, 478 — 90% — were preceded by a sleep breathing event: an apnea, a hypopnea, or a respiratory effort-related event [s3]. The remaining 53 were attributed to independent leg jerks (7), were spontaneous (14), or were induced by the laboratory environment (32) [s3]. Every one of the thirty awakenings lasting five minutes or longer — a duration the authors describe as sufficient to predispose toward an insomnia episode — was preceded by a breathing event [s3].

This is twenty patients at one centre, selected for treatment-seeking chronic insomnia, with no control group. It is a pilot study and the authors present it as one. It cannot be generalised to the third of the population who wake at night, most of whom are not seeking treatment for insomnia at all.

What it does do is puncture a specific assumption: that a person waking in the night knows why. In this small series, the patients' accounts and the polysomnography disagreed almost completely [s3].

The shape of the honest answer

Waking during the night is normal and extremely common [s1] [s2]. Persistent difficulty getting back to sleep is neither, affects a much smaller group, and is where the measurable daytime impairment sits [s2]. And the reasons a person gives for their own awakenings are, at least among treatment-seeking insomnia patients studied in a laboratory, an unreliable guide to what a recording shows [s3].

That combination is a case for asking a clinician rather than for self-diagnosis, particularly given how strongly nocturnal awakening in these surveys tracks with treatable physical conditions [s1] [s2]. This article describes what the studies found and is not medical advice.

Sources

• Nocturnal awakenings and comorbid disorders in the American general population — Journal of Psychiatric Research, 2008-03-28
• Nocturnal awakenings and difficulty resuming sleep: their burden in the European general population — Journal of Psychosomatic Research, 2010-04-28
• Prospective assessment of nocturnal awakenings in a case series of treatment-seeking chronic insomnia patients: a pilot study of subjective and objective causes — SLEEP, 2012-12-01