Insomnia: what happens in the nervous system when the brain won't let go of the day

It’s three in the morning. Your body is exhausted, but your thoughts are running as if it were the middle of a working day: the conversation that stung, the list of things to do, the worry about how you’ll function at all tomorrow. You glance at the clock and start calculating: “If I fall asleep now, I’ve still got four hours.” Twenty minutes later, again: “Three and a half hours.” Do you know this feeling?

You’re not alone. Research suggests that roughly a third of adults experience symptoms of insomnia at least occasionally, and in about one in ten it becomes chronic — a condition that colours a whole life, not just the nights. And above all: there is nothing wrong with you. Your nervous system is simply doing what it is convinced keeps you safe.

In this piece I explain what is actually happening in your body and brain during insomnia. Not because knowledge is a sleeping pill in itself, but because understanding is the first step: once you know what is going on, you can stop fighting sleep — and start working with it.

Insomnia isn’t a choice — it’s a state of readiness

First, let’s clear up something important: nobody lies awake because they haven’t tried hard enough to fall asleep. If anything, the opposite is true — most people with insomnia try harder than anyone. The problem lies elsewhere.

Sleep requires two things: enough sleep pressure (the tiredness that builds up over the day) and a nervous system that judges it safe to let go of control. It’s the second one that usually gets stuck in insomnia.

Our autonomic nervous system has two main modes: the sympathetic, which prepares us for action (“fight or flight”), and the parasympathetic, which looks after rest, digestion and repair. During the day a degree of sympathetic activation is perfectly healthy — it helps us work, respond, stay focused. In the evening, though, the parasympathetic should take the wheel: the heart rate slows, the muscles let go, thoughts soften and sleep comes of its own accord.

But if the day has been full of tension — or if the nights themselves have become a source of stress — the sympathetic system stays switched on. Science calls this hyperarousal, and it is one of the most robustly confirmed findings in the field of insomnia: in people with chronic insomnia, researchers consistently measure a higher heart rate and lower heart rate variability, a higher body temperature, raised cortisol, faster metabolism and more “awake” brain waves — not only in the evening, but throughout the day, and even during sleep itself. Put simply: at night the body stands guard instead of resting.

This also explains a familiar paradox: many people with insomnia can barely keep their eyes open on the sofa at eight in the evening, yet the moment they lie down in bed they are wide awake. The sleepiness was real — but for their nervous system the bed has become a signal for alarm, not for rest.

Two systems that regulate sleep

To complete the picture, you need one more basic model, the one science uses to explain sleep. It is called the two-process model (Borbély, 1982), and it says that sleep is regulated by two independent processes.

The first is homeostatic sleep pressure. From the moment you wake, a substance called adenosine — a by-product of energy use — accumulates in the brain. The more hours you are awake, the more of it there is and the stronger the need for sleep. Sleep “clears” the adenosine and the counter resets. (Incidentally: coffee works by occupying adenosine receptors — it hides the tiredness, it doesn’t remove it.)

The second is the circadian rhythm, the internal clock in the brain that uses light to determine when the body is set for wakefulness and when for sleep. In the evening, as it grows dark, the pineal gland begins releasing melatonin — the hormone that tells the body night is coming.

In healthy sleep the two processes work together: in the evening sleep pressure is high and the internal clock opens the “sleep gate”. In insomnia, though, this often happens: hyperarousal drowns out both. Sleep pressure is high, the clock says night — but the alarm in the nervous system is stronger than either. Which is why you can see why advice like “go to bed earlier” doesn’t work: the problem isn’t the clock, it’s the alarm.

What happens in the brain when you don’t sleep

A sleepless night isn’t just unpleasant — it also changes the way the brain processes the world the next day.

In a well-known study, Yoo and colleagues (2007) deprived healthy participants of sleep for one night and then showed them emotionally arousing photographs in an MRI scanner. The result: the amygdala, the brain’s threat-detection centre, responded roughly 60 per cent more strongly than in rested participants. At the same time its connection with the prefrontal cortex weakened — the part of the brain that calms emotions, puts them in context and regulates them. The researchers wrote that the sleep-deprived brain behaves as if the brakes had been disconnected.

This explains why everything looks harder after a bad night: a small clumsiness becomes a catastrophe, an ordinary comment an insult, tomorrow’s meeting a mountain. And because being flooded with emotion is itself new stress, the circle closes — the worse you sleep, the harder it is to settle; the harder it is to settle, the worse you sleep.

Something else is going on alongside this: at night, during deep sleep, the brain does its “cleaning”. The lymph-like glymphatic system flushes out metabolic waste most efficiently then, memories are consolidated, and the emotional charge of the day’s experiences is turned down. Matthew Walker, one of the leading sleep researchers, vividly calls dreaming sleep (the REM phase) “overnight therapy”: in it the brain replays emotional experiences, but without noradrenaline — the stress chemistry — and so gradually takes the sting out of them. When sleep is missing, this nightly processing doesn’t happen and emotions stay “raw”.

The vicious circle: how one bad night becomes chronic insomnia

All of us sleep badly at some point — with stress, illness, a big change, caring for someone close to us. That is normal and as a rule it passes by itself once the trigger has passed. The trouble starts when a web of worries and habits forms around the bad nights, one that keeps the insomnia going even after the original trigger is gone.

Psychology describes this with Spielman’s three-P model (1987), which to this day remains the foundation for understanding chronic insomnia:

• Predisposition: some of us naturally have a more excitable nervous system, are more finely tuned, more inclined to worry. That is not insomnia in itself — but it is the ground in which it takes root more easily.
• Precipitation (the trigger): a stressful event that actually disrupts sleep — a loss, a conflict, a move, an illness, the birth of a child.
• Perpetuation (what maintains it): everything we start doing in order to help ourselves that in fact keeps us awake — going to bed early, naps, coffee, counting the hours, working from bed, checking “sleep instructions” in the evening.

The key message of this model: chronic insomnia is usually maintained not by the original stress, but by our relationship with sleep, which has changed in the meantime. The bed is no longer a place of rest but the scene of a struggle. And that is precisely why insomnia is so treatable — what maintains it can be changed.

What insomnia does to your day

We usually talk about insomnia as a night-time problem, but its real cost is paid during the day. You may recognise some of this:

• Concentration and memory: you read the same sentence for the third time, you forget names and arrangements, work that would take you an hour when rested takes three.
• Emotions: a lower threshold for anger and tears, more anxiety, less patience with the people you love. Research consistently links poor sleep with greater emotional reactivity after just a single night.
• The body: chronic lack of sleep is associated with a weakened immune response, a bigger appetite (the balance of the hormones leptin and ghrelin is disrupted) and, over the long term, a higher risk of cardiovascular and metabolic disease.
• Relationships: perhaps the most painful — an exhausted person withdraws, is irritable, has no energy for closeness. Insomnia is often a matter for relationships too, not just for the individual.

I’m not writing this to frighten you — fear of the consequences of insomnia is, ironically, one of the things that maintains it best. I’m writing it because you deserve to know that your daytime exhaustion is not laziness or weakness. It is the logical consequence of nights in which your system doesn’t get its repair. And it is a reason why it’s worth doing something — not with even more effort, but differently.

Why “try harder to fall asleep” doesn’t work

Sleep is one of the few processes you move further away from by trying. You can’t decide to fall asleep the way you decide to raise your hand. All you can do is set up the conditions and allow it to happen.

The psychologist Colin Espie and colleagues described this mechanism as the attention–intention–effort pathway: a good sleeper doesn’t think about sleep at all; a person with insomnia watches sleep (attention), deliberately wants it (intention) and works at it (effort). Each of these three steps pushes sleep further away, because each means activation — and activation is the physiological opposite of falling asleep. There is even a questionnaire, the Glasgow Sleep Effort Scale, and scores on it nicely predict who has more trouble with insomnia.

Which is why, paradoxically, the opposite helps: allowing yourself to be awake. In behavioural therapy there is a technique called paradoxical intention — instead of trying to fall asleep, you try to stay calmly awake (eyes open, no screen, no work). Once the pressure that you must fall asleep drops away, the nervous system can settle — and sleep arrives by itself, through the side door.

Sleep myths that feed insomnia

A few beliefs I hear again and again in my work with people — and which research does not support:

• “Everyone needs 8 hours.” The need for sleep is individual; most adults need between 7 and 9 hours, some get by on less. A rigid number becomes the measure you punish yourself with at night.
• “If I can’t sleep at night I should stay in bed so at least I’m resting.” Lying there in wakeful tension strengthens the bed–wakefulness association. Behavioural guidelines advise exactly the opposite: if you can’t sleep for a long stretch, get up and come back when you feel sleepy.
• “I’ll catch up at the weekend.” Sleeping late at weekends shifts the internal clock (an effect similar to jet lag) and Sunday night is often the worst of the week.
• “A glass of wine helps me fall asleep.” Alcohol brings sleep on faster, but it fragments the second half of the night and suppresses precisely the dreaming sleep that does the emotional repair.
• “After a bad night I have to cancel the day.” Cancelling activities gives insomnia ever more power over your life — and more empty space for worry.

What actually helps

The good news: chronic insomnia is among the best researched and most treatable mental health problems. American and European clinical guidelines agree: the first-line treatment is not a pill but cognitive behavioural therapy for insomnia (CBT-I). In research its effects are comparable to sleeping tablets in the short term and better in the long term — and unlike tablets, they last after treatment has ended.

CBT-I works on exactly the maintaining factors from the circle above. Here are some of its key components, to give you a sense of where this path leads:

• Stimulus control: the bed becomes a place for sleep (and intimacy) only — not for work, screens, brooding or lying awake.
• Adjusting the sleep window: a temporarily shorter but more consolidated time in bed, so that sleep becomes denser and confidence in it returns; then the window is gradually widened.
• Working with worry: worries get their own slot during the day (“worry time”), and paper and pencil by the bed make sure thoughts don’t need to circle until morning.
• Restructuring beliefs: exactly those myths from the previous section that turn a bad night into a catastrophe.
• Settling the body: techniques that address hyperarousal directly — a lengthened out-breath, progressive muscle relaxation, an evening wind-down without screens.

Sleep hygiene (darkness, cool, rhythm, less caffeine) is a useful foundation for all of this — but on its own it does not usually resolve chronic insomnia. If it did, you probably wouldn’t have had it for this long.

Insomnia as a message

From my therapeutic experience I’d add one more layer that the protocols don’t always capture: insomnia is often a message. Through it the body says that something in your life is asking too much and giving back too little — a relationship, a pace, a profession, an unresolved story, grief that had no room.

The night, after all, is the first moment of the day when all external demands go quiet. What we successfully push aside during the day gets the stage at night. That’s why, when working with insomnia, we almost always also talk about what is waiting for you at night once the world falls silent — and it often turns out that sleep is not the problem but the messenger. I know this from close up too: for years I lived with chronic insomnia, and it was insomnia that eventually brought me to psychotherapy. I’ve written about everything it taught me in a separate piece.

When to seek help

We speak of chronic insomnia when sleep problems last at least three months, occur at least three nights a week and noticeably affect your day. If you recognise yourself in this, don’t wait for it to pass on its own — the sooner you break the vicious circle, the easier it is to break.

Where can you turn? To your GP (also so that between you, you can rule out physical causes such as sleep apnoea or thyroid problems), to a therapist trained in working with insomnia, or to me — especially if you sense that your wakefulness is not just a technical problem but has something to say. My own story with sleep is described on the my approach page; and for more on what traumatic experiences do to the nervous system (a mechanism often related to insomnia), see the piece on the myth “what doesn’t kill you makes you stronger”.

Until then, perhaps just this tonight: when you wake at three again, instead of “here it goes again”, try saying “my body is standing guard — and nothing is missing if I just lie here and breathe”. This is not magic. But it is the first step out of the struggle.