How Sleep Works: Understanding Why You Can't Sleep

Why Can't I Sleep?

sleeping in a bed seeing toes

It's one of the most common questions I hear.

And it's usually asked with a mixture of frustration, exhaustion and sometimes a little bit of fear.

"Why can't I sleep?"

"What am I doing wrong?"

"Why does everyone else seem able to sleep except me?"

The problem is that most people are looking for one answer.

One cause.

One thing to fix.

But sleep doesn't really work like that.

When somebody tells me they can't sleep, there are three things I'm immediately thinking about:

• Sleep pressure

• Circadian rhythm

• Nervous system state

Because sleep isn't one thing.

It's a system.

And when one of those systems isn't working as well as it could, sleep can start to feel difficult.

Understanding those three systems can completely change how you think about your sleep.

More importantly, it can help you stop blaming yourself.

How Sleep Works

One of the biggest misconceptions about sleep is that it simply happens when we get tired.

In reality, sleep is driven by several biological systems working together.

Think of it like this.

Your body needs the right amount of sleep pressure.

It needs a circadian rhythm that knows what time of day it is.

And it needs a nervous system that feels settled enough to allow sleep to happen.

When these systems are working together, sleep often feels easy.

When they're not, sleep can start to feel like hard work.

And sleep was never meant to feel like hard work.

You can force yourself to wake up.

You can't force yourself to sleep.

That's the whole thing.

Sleep Pressure: The Drive Behind Sleep

The first part of the sleep system is sleep pressure.

Sleep pressure starts building from the moment you wake up.

The longer you've been awake, the more pressure builds.

That pressure is what helps you fall asleep.

It's what helps you stay asleep.

It's one of the most important drivers of sleep.

One of the ways I encourage people to think about this is to stop asking:

"How much sleep do I need?"

And start asking:

"How long do I need to be awake before sleep feels easy?"

Because sometimes we're so focused on sleep itself that we forget the role wakefulness plays in creating it.

Sleep pressure builds throughout the day.

Which means tonight's sleep is often influenced by what happened this morning.

Not just what happens at bedtime.

What Can Affect Sleep Pressure?

Several things can reduce the amount of sleep pressure available when bedtime arrives.

These include:

• Daytime naps

• Excessive caffeine

• Spending long periods inactive

• Sleeping in at weekends

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This doesn't mean these things are always bad.

It simply means they can influence how much sleep pressure is available later in the day.

On the other hand, regular movement throughout the day can help support the natural build-up of sleep pressure.

I'm a big fan of what I call movement snacks.

Small moments of movement throughout the day.

Nothing dramatic.

Just enough to keep the day moving forwards.

Circadian Rhythm: Your Internal Body Clock

The second part of the sleep system is your circadian rhythm.

This is your body's internal timing system.

Think of it like the operating system running quietly in the background.

It's constantly collecting information about what's happening around you.

Light.

Food.

Movement.

Wake-up times.

Daily routines.

It's paying attention all the time.

Not perfection.

Rhythm.

This is why I'm often much more interested in what time you're waking up than what time you're going to bed.

Because when you wake up at a similar time each day, sleep pressure starts building from the same point each day.

Over time, your body begins recognising that pattern.

For many people, sleepiness naturally starts emerging around 16 to 17 hours after waking.

Not because you've forced it.

Because your body knows what's coming next.

Why Consistency Matters for Circadian Rhythm

When your wake-up time changes dramatically from day to day, your circadian rhythm receives mixed messages.

It's a little bit like constantly changing the time on a clock.

The system becomes less predictable.

The more predictable your mornings become, the easier it is for your body to understand what it's meant to be doing.

And that includes sleeping.

Why Your Nervous System Matters for Sleep

This is the piece that often gets overlooked.

You can have good sleep pressure.

You can have a reasonably well-regulated circadian rhythm.

And still struggle with sleep.

Because sleep also relies on your nervous system.

Now when I say your nervous system needs to feel calm enough for sleep, I don't mean you need an empty mind.

I don't mean you need to be completely relaxed.

Life doesn't work like that.

But sleep does require your body to feel settled enough to let go.

If you've got a lot of stress.

If you've got a lot on your mind.

If your system is running on high alert.

That can absolutely influence your sleep.

Sleep and alertness are competing states.

The more activated your nervous system feels, the harder it can be for sleep to emerge naturally.

This is often why people tell me they're exhausted but can't sleep.

Their body is tired.

But their system is still alert.

Why Sleep Problems Happen

This is where things start to make sense.

Sleep problems don't always happen because you're doing something wrong.

And they don't happen because you've forgotten how to sleep.

Often, one of these systems simply isn't working in harmony with the others.

You might have:

• Strong sleep pressure but an activated nervous system

• A healthy circadian rhythm but insufficient sleep pressure

• Good sleep pressure and circadian timing but a nervous system that feels constantly on alert

  
  

When one part of the system struggles, the whole experience of sleep can change.

That's why sleep advice works brilliantly for some people and not at all for others.

The advice isn't necessarily wrong.

It may simply be targeting the wrong system.

Why Understanding Your Sleep System Changes Everything

One of the biggest shifts I see in clients isn't necessarily that they sleep better immediately.

It's that they understand.

They understand why their sleep is happening.

They understand what their body is doing.

They understand which lever might need attention.

And when that understanding arrives, something changes.

The anxiety softens.

The pressure eases.

The fear starts to reduce.

Because sleep becomes less personal.

Less emotional.

Less about blame.

And more about biology.

You Are Not Broken, Your Sleep System May Be Stuck

If you've been struggling with sleep for a while, it's easy to start believing something is wrong with you.

I hear it all the time.

"I've always been a bad sleeper."

"There must be something wrong with me."

"I've tried everything."

But what if that's not true?

What if your body still knows exactly how to sleep?

What if your sleep system is simply stuck?

Because that's what I see far more often.

Whenever I assess somebody's sleep, I'm looking at three things:

• Sleep pressure

• Circadian rhythm

• Nervous system state

  
  

Because those are the systems that create sleep.

And when we understand them, sleep starts to make a lot more sense.

If you take nothing else away from this article, take this:

You are not broken.

Your body knows how to sleep in the same way it knows how to breathe.

Sometimes the system just needs a little help finding its rhythm again.

Sleep will always, always find you.

Ready to Understand Your Sleep Better?

If you'd like to understand your own sleep patterns more clearly, start by tracking what your sleep actually looks like.

My Interactive Sleep Diary helps you visualise your sleep over time so you can begin to see patterns that might otherwise be missed.

Because sometimes the first step isn't changing your sleep.

It's understanding it.