Why your weekend lie-in might be leaving you exhausted

Oversleeping on lazy Sundays might seem blissful, but it can leave you feeling groggy and lethargic. Photo / 123rf

Planning to catch up on your sleep debt this weekend? Many of us enjoy extra hours in bed on a lazy Sunday, but scientists have found it may be worse for your mental sharpness.

It’s Sunday morning and there’s no need to get out of bed. What could be nicer, then, than sticking a metaphorical finger up at the alarm clock, scrunching the duvet around you and drifting back to sleep until 11am.

But you won’t be alone in finding that these extra hours of sleep can have a surprising, counterintuitive effect. Rather than leaving you clear-headed and sharp, “oversleeping” can make a person feel groggy and lethargic for the rest of the day – and beyond.

It turns out there’s a proper scientific reason behind this muzzy head. Because, while the majority of studies have focused on the very real – and generally more distressing – consequences of too little sleep, or insomnia, there is an increasing body of research about the health downsides of sleeping too much.

In 2018, neuroscientists at Western University in Ontario studied 10,000 participants who recorded their own typical sleeping patterns. They then took a cognitive test, which comprised short-term memory tasks, verbal reasoning and spatial planning exercises.

The subjects reported the optimal amount of sleep for reasoning, verbal and “overall ability” was between 7.16 and 7.38 hours (well within the sleep “sweet spot” discussed below). Perhaps unsurprisingly, the researchers found that regularly getting fewer than seven hours of sleep negatively affected the performance of the participants in the test.

Having a bit of extra sleep – around an hour – was seen to be beneficial. “However, we also found sleeping more than 2.76 hours more than usual was associated with decreasing performance,” said Adrian Owen, the lead researcher. “This impaired cognition seen in long sleepers is actually driven by too much sleep; for example, longer sleep is associated with longer and more intense ‘sleep inertia’.”

Dr Sophie Bostock is a behavioural psychologist and sleep scientist. It’s this “sleep inertia” that gives us the Sunday-afternoon brain fog, she says. “Our body clock is based on a set of genetically hard-wired instructions with a 24-hour rhythm,” says Dr Bostock. “We are biologically programmed to do the same things at the same time: to start moving, eating and interacting socially. When our clocks get confused and are thrown out of sync, scientists call this ‘circadian disruption’. We still can operate, but are slightly sub-par.”

According to Dr Bostock, this disruption can also spill over into the following day.

“If you haven’t had enough time awake on a Sunday, you won’t have enough of what we call ‘sleep pressure’ or the drive to fall asleep,” she says. “A late start might leave you feeling ‘wired’ and you won’t fall asleep as easily.” It can also lead to a woozy Monday morning.

In addition, studies report that if you consistently need extra sleep, it might indicate other problems. A large French project from 2016 defined “long sleep” as more than 10 hours (it defined “short sleep” as fewer than five.) “In the general population, sleeping too much was associated with psychiatric diseases and higher BMI (body mass index) – though not other chronic medical diseases,” the study found.

Interestingly, the paper deduced that “long sleepers” were often female and from two age groups – between 15 to 25 years, or over 65, without university degrees.

However, the authors were keen to point out that these results could be due to “reverse causation in the interpretation” – that people tended to sleep for a long time because they had health problems, and not the other way around. The study also pointed out that staying in bed too long could lead to depression, failing health, increased morbidity risk and decreased physical fitness.

‘We don’t fully understand it’

Guy Leschziner is a professor of neurology and sleep medicine at Guy’s and St Thomas’ NHS Trust. “We’ve known for many years that if you sleep for more than nine hours a night, you might be at increased risk for serious health issues,” he says. “We don’t fully understand it, but sleeping longer could mean you have other things going on. It could be a marker for illnesses like cardiovascular disease or stroke, or even early signs of neurodegenerative diseases such as dementia.”

Professor Leschziner adds that long, unrefreshing nights in bed can also be signs of less serious conditions such as obstructive sleep apnoea (a nocturnal breathing disorder) or periodic movement limb disorder – both eminently treatable by a doctor.

So how much should we be sleeping? A 2019 paper published in Harvard Health concluded that a minimum of seven hours is recommended for good health. The research was based on hundreds of studies that followed people’s long-term experience of heart disease, diabetes and mental health difficulties. Those who slept between seven and nine hours were typically at lower risk of becoming sick in the future.

However, experts such as Dr Bostock agree that your own sleep sweet spot might fall outside this calculation.

“Sleep duration can depend on various factors, including your genetic makeup, age and lifestyle,” she says. “Just like your shoe size, ‘optimum sleep’ varies from person to person. For example, some people have a ‘short sleep’ gene. Whether you feel refreshed after six hours or eight, chances are you are getting enough rest.”

As for those Sunday lie-ins, there’s no need to panic that you are doing yourself permanent damage or have a serious underlying health issue. According to Professor Leschziner: “If you’re having a once-a week lie-in, it probably only demonstrates you aren’t having enough sleep. But if you are continuously sleeping for many hours, and are waking up unrefreshed, it’s probably an idea to talk to your GP.”

Research suggests that too much sleep can impair cognitive function, leading to a phenomenon known as "sleep inertia". Photo / 123rf

The good news is that the once-a-week lie-in fog is easily reversed. “Our study suggests that people who have chronically too little or too much sleep might see a cognitive improvement with as little as one night of better sleep,” says Adrian Owen of Western University.

Dr Bostock agrees. “Your cognition begins to recover as sleep duration returns to normal,” she says. “After a long week of early mornings and broken nights, you may well have a ‘sleep debt’ that needs paying off, and that’s fine. But the trick is to get back to consistent nights as soon as possible.”

The Insomnia Diaries: How I Learned to Sleep Again by Miranda Levy is published by Octopus Books.

How to get the benefits of great sleep without oversleeping

All sleep experts agree that it’s the quality of sleep – whether your sleep is restful and restorative – that is important, not the quantity. Sleep quality is based on factors such as sleep latency (the time it takes you to fall asleep), and how often you wake up during the night. Here’s how to keep high quality sleep:

Do: keep a consistent night time routine

Whatever time you habitually go to bed and wake up in the morning, try to stick to this routine. According to a paper published in the journal Sleep, in January 2024: “Research demonstrates that sleep regularity, the day-to-day consistency of sleep-wake timing, can be a stronger predictor for some health outcomes than sleep duration.”

Do: check your sleep hygiene is good

The basic stuff, but it’s important. So, sleep in a dark, quiet room, with a temperature of between 18 and 21 degrees. A cooler room is better for sleep: “I never have the heating on in my bedroom, even in the winter,” says Dr Bostock. Don’t drink coffee within six hours before bed, and keep any naps to a minimum.

Quality of sleep is more important than quantity, with factors like sleep regularity and sleep hygiene playing key roles. Photo / 123rf

Don’t: be fixated by your sleep tracker

Becoming wedded to your sleep tracker can cause a condition the experts call “orthosomnia” – the pursuit of perfect sleep.”Anything that draws attention to sleep can make it worse,” says Prof Leschziner. “This is why people fall asleep while watching TV or reading a book. They are distracted. If you know you have poor quality sleep, and the tracker confirms this, it won’t help, but will only increase your anxiety.”

Don’t: worry if you wake up a lot at night

Sleep is not uniform. An average person on an average night cycles through four stages, four to six times a night. Sleep cycles are not always the same length, but on average they last about 90 minutes each. “It doesn’t matter if you wake up during the night,” says Dr Bostock. “Your sleep goes in 90-minute cycles, and people tend to wake up more as they get older.”

Don’t: turn your bedroom into a battleground

After a run of a few bad nights, it’s easy to dread going to bed. But, says Dr Bostock, this is counterproductive. “Instead of telling yourself ‘that’s it, I’m never going to sleep again,’ reassure yourself: ‘I’m a good sleeper, I’m just having a bad night’.”