Waking up in the night

Waking in the night is a normal feature of human sleep, not a fault in it. A healthy night is built from cycles with brief arousals at the joins, and surfacing once or twice far enough to notice is ordinary at any age and increasingly ordinary with age. Around a third of adults report it most weeks.

So the useful question is not whether you woke. It is whether you went back, and whether the next day paid for it. Those two are what separate an uneventful night from a complaint, and neither of them is a count of awakenings.

Sleep is not a flat state you drop into and climb out of. It runs in cycles of roughly ninety minutes, and the composition of those cycles changes as the night goes on: deep slow-wave sleep is concentrated in the first third, and the later part of the night is lighter, with more REM and more time close to the surface.

Brief arousals happen several times an hour throughout, and a sleep laboratory scores them as a routine part of a normal recording. What decides whether you know about one is duration, not depth — an arousal has to last on the order of a minute or two before any memory of it is laid down. Most of the night's awakenings are therefore invisible to the person having them, which is the single most important thing to know before counting your own.

That the second half of the night is the thin part also explains the timing people report. Waking at four is not a message. It is the hour at which there is least deep sleep left to hold you under.

There is an older and much-quoted idea that human sleep was once routinely split into two blocks with a waking interval between them — historical evidence from Ekirch, and a laboratory echo in Wehr's work on long winter nights. It is worth one sentence and not a theory of your night: what it does establish is that an unbroken block was never the biological standard it is now assumed to be.

Three things, and the number of awakenings is not among them.

How long you are awake, totalled. The working clinical line is about thirty minutes of wakefulness across the night, on three or more nights a week. Lichstein's group found that cut separated ordinary nights from clinical patterns, and it is phrased as a total for a reason: four awakenings of two minutes each is a normal night, and one awakening of ninety minutes is not.

Whether the following day pays. Fatigue, a mind that will not hold a thread, irritability, a shortening fuse by mid-afternoon. A waking with no cost attached does not meet the definition of anything, which is the clause the entry on insomnia exists to spell out.

What happens in the gap. This is the part that converts a biological event into a condition. You wake, which was always going to happen, and then you do arithmetic — four hours and ten minutes until the alarm, the meeting at nine, how bad tomorrow will be. That calculation is arousal, and arousal is what keeps you out of sleep for the next hour. The waking was ordinary. The hour was not, and the hour is the thing treatment works on.

Sorting out what wakes you in the first place — body, mind, rhythm, room — is its own piece of work, and it is done properly in why do I wake up at 3am every night.

This is the finding that most changes how the night reads, and it is not a polite way of saying someone is exaggerating.

Put a person who reports having barely slept into a sleep laboratory and the recording routinely shows several hours of sleep. In its extreme form it has a name in the diagnostic manual — paradoxical insomnia, where the gap between what was recorded and what was reported is the defining feature — but a milder version of the same mismatch is the normal case in insomnia rather than the exception.

Two mechanisms do most of it, and they are both ordinary.

Light sleep does not feel like sleep. The shallow stages that dominate the second half of the night are experienced from the inside as lying there with your thoughts. Woken out of them, people say they were awake, and they are reporting honestly.

Only wakefulness gets encoded. You cannot remember the time you spent asleep, so a night is reconstructed out of the fragments you were awake for, and three ten-minute wakings separated by sleep you have no record of assemble into a single impression of a night spent awake. Harvey and Tang's review set out how time estimation in the dark, attention trained on any sign of not sleeping, and the absent memory of sleep produce that result between them.

Why it matters is not accuracy for its own sake. The belief that you got nothing is what produces the dread of the coming night, and the dread is what lengthens tomorrow's wait. One of the quiet mechanisms of recovery is simply learning that the night held more sleep than it felt like.

• Do not look at the clock. It supplies the number the arithmetic runs on, and there is nothing you can do at three with the answer.
• If the wait becomes frustration, get out of the bed. This is stimulus control, and the point is to stop the bed from being the place where you lie awake; the reasoning is in the entry on CBT for insomnia.
• Do not make it up afterwards. A long lie-in and an afternoon nap widen the opportunity without adding sleep, which is how one broken night becomes a pattern.
• Write a fortnight down. Rough time awake, not number of awakenings, plus one line on the day. That document is what any assessment is built from.

A short list worth raising with a doctor rather than solving at night: snoring with witnessed pauses in breathing or gasping, which points at apnoea and is the commonest treatable cause of a fragmented night; an urge to move the legs that moving relieves; pain; reflux; hot flushes around menopause; alcohol, which sedates the first half of the night and breaks up the second; and waking repeatedly to pass urine, which is as often a consequence of being awake as a reason for it.

If the nights started after an argument rather than after a change in health, that is a different mechanism and why can't I sleep after an argument is about it specifically.

MoodyWonder's Night Waking test asks how long you are awake and what the day costs rather than how many times you surfaced, because the count was never the variable. It is a screening-style read, not a diagnosis.