What happens when you don’t sleep?

Key Points

• Sleep is vital for almost every system in the body to function well
• The glymphatic system clears toxins from the brain while we sleep
• It’s important not to overcompensate when you’ve missed sleep

Ever missed a night of sleep and felt foggy, tired, grumpy and lacklustre the next day? It happens to the best of us. While some people can function reasonably well after a bit of missed sleep, others may feel the effects after just one night. And since sleep is fundamental to good health, prolonged sleep deprivation can take its toll.

Whether your lack of sleep is self-inflicted or you’re having trouble getting to sleep (and staying asleep), there are many potential effects of sleep deprivation on your brain and body.

We spoke with Dr Moira Junge, healthylife Advisory Board member, CEO of the Sleep Health Foundation and a registered practising health psychologist, to find out exactly what happens when you don’t sleep and what to do about it.

What effects can a lack of sleep have on the brain?

The ‘glymphatic system’ is the brain’s very own waste elimination system. While it’s generally dormant during the day, the glymphatic system comes to life as you rest – if you’re struggling to get enough zzz’s consistently, toxins may build up over time leading to decreased or impaired function. A lack of sleep can affect the brain in the following ways: 

• Impaired cognitive performance, including slow thinking, poor memory and reduced attention spans
• Mood changes
• Decreased reaction times
  

And if you’re thinking of driving when you’re sleep deprived, take a moment to consider the following insight from Dr Moira.

“If you’ve been awake for 17–19 hours. It’s the equivalent of having a blood alcohol reading of 0.05.”

What effects can a lack of sleep have on the body?

Good sleep doesn’t only influence a happy, healthy brain, it’s actually essential for almost every system in the body to function well, so missing out can impact your organs, energy levels and more in numerous unseen ways. While you’re deep in the sleep cycle:

• Hormones, such as growth hormones, are being released, which help your tissues repair themselves.
• Your sympathetic nervous system is relaxing.
• Your immune system is releasing proteins called ‘cytokines’ to help fight inflammation.

And if your body can’t rest and repair during your downtime? You could struggle with things like an impaired immune and nervous system, changes to your endocrine system, gastrointestinal disorders and an increased risk of chronic health disorders. Not to mention a general feeling of not having enough energy. 

“You’re also just physically tired, so you can’t move as much,” says Dr Moira. “You have less motivation for moving your body.”

Fatigue vs. tiredness vs. sleepiness

It goes without saying that if you don’t get enough sleep, you may feel tired. But what’s the difference between fatigue, tiredness and sleepiness?

Fatigue is defined as ongoing weariness from bodily or mental exertion. It’s more than just feeling tired, which is a feeling that usually passes after you have a good sleep. Sleepiness is slightly different.

“Sleepiness is when you’re yawning, your eyes are tired and heavy, and you feel like sleep is imminent,” says Dr Moira.

“Sleepiness just means you need more sleep – it’s a signpost your sleep quality is poor. General tiredness or fatigue, however, could be related to issues with your thyroid, stress levels, quality of dietary pattern and how much iron you’re getting in your diet.”

And when it comes to weariness overall, Dr Moira asks the important question.

“Are you getting enough rest during the day? Are you taking the time to wind down rather than work, work, work?”

What causes a lack of sleep?

There are multiple reasons why people don’t sleep, and according to Dr Moira, they can be categorised into societal and individual factors.

“It’s not just personal preferences around how much priority someone gives to sleep. We need to consider someone’s social circumstances such as how much support they’re getting, their financial status, how much they have to travel, the kind of housing they’re in, whether they live in a noisy area.”

Along with these environmental factors that may lead to a lack of sleep, individual considerations include:

• not prioritising sleep
• sleep disorders
• a racing mind or anxiety
• shift work
• too many stimulants (alcohol, caffeine, nicotine)
• stress
• screen time before bed
• medical conditions and pregnancy
• side effects of medication

How long can you go without sleep before it damages your health?

Dr Moira says no one can pinpoint exactly how long it takes for sleep deprivation to seriously affect your health. What we can say, however, is that the effects may begin immediately.

“We’re not advanced enough to know the precise answer to this question,” she explains. “Some people are fine and have a bit of a buffer. Whether they get five hours or eight hours, they’re good. But I know myself, even after one night of poor sleep, I’m a bit of a wreck. I’m snappy or a bit teary.”

And it’s worth noting that when you feel like you’ve had zero sleep, you may actually be asleep without realising it.

“Clinically, people have come to me and said, ‘I haven’t slept for three weeks, not a wink’. And we know that if we put some electrodes on their heads, they would sleep when they thought they were awake.”

How long does it take to catch up on missed sleep?

It depends on the individual, how long they’ve been sleep deprived and what their personal sleep needs are, according to Dr Moira. Some people may bounce back quickly after one sleep, and others may take longer.

One study found that some people who accumulate sleep debt during the week may be able to catch up on sleep over the weekend.

“You can’t really catch up in terms of getting that lost sleep back immediately, but you will get back on an even keel within a few days and not necessarily have long-term harm,” Dr Moira explains. 

But she cautions against overcompensating.

“It’s important not to jump back into overcorrection because that will upset the apple cart for sure,” she says. “You still need to create 16 hours of wakefulness to get eight hours of sleep.”

“It’s OK to take a quick 20-minute nap during the day. But if you sleep through until 1pm on a Sunday, you won’t necessarily feel sleepy enough at the right time on Sunday night to set yourself up for the week.”

Good sleep for good health

It’s clear skipping sleep doesn’t do your body or brain any favours. If you routinely miss out on quality sleep, it may be worth evaluating what changes you could make to ensure you prioritise your sleep needs. 

If you find getting to sleep or staying asleep challenging, there’s plenty of help available. Chat with your healthcare professional for advice.

Related:

• 7 aids for a restful night’s sleep
• What does revenge sleep procrastination mean?
• Understanding your circadian rhythm

Dr Moira Junge, a healthylife Advisory Board member, is a registered practising health psychologist with the added specialty of sleep. She has been in private practice for over 20 years and is the CEO of the Sleep Health Foundation and was a founding member of the Behavioural Management of Sleep Disorders Committee within the Australasian Sleep Association (ASA). Dr Moira was also Chair of the ASA Insomnia and Sleep Health Council (2008-2015) and is a full member of the Australian Psychological Society.

Reviewed by the healthylife Advisory Board May  2023.