It’s your perception of sleep that’s making you feel tired all day

New Scientist · Feb 23, 2026 · Collected from RSS

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James Steinberg If you slipped under the covers at 2am, knowing your alarm was set for 6am, how do you think you would feel the next morning? You may be imagining a day of aching eyes and clouded thoughts, but it is perfectly possible to wake up feeling clear-headed and positive, then spend the day happily socialising, or even doing a spot of exercise. For most of us, this sounds like a dream. We live in a world obsessed with how little sleep we get and how rubbish that makes us feel. Many of us chase solutions – wearing eye masks, using blue-light filters, eating sleep-boosting probiotics – all in the pursuit of that golden 8 hours of sleep. But what if the secret to feeling restored has little to do with how much we have actually slept? A wave of new research is suggesting that, in many cases, the way we think about sleep matters more than the hours we get. Simply believing you are well-rested can be enough to create the positive mental and physical benefits of a peaceful slumber. The question then becomes, how do you trick yourself into thinking you have slept better than you have? The answer may be easier than you think. The power of mindset The idea that a simple shift in perspective can leave you feeling rested might sound absurd, but two decades of research have established that mindset has a powerful influence on our health and behaviour. Teaching children to embrace a growth mindset – the belief that their abilities can improve with learning – is now common practice in UK schools after studies showed that young people who viewed their mind as malleable, rather than fixed, coped better with failure and were more willing to take on new challenges. Likewise, a person’s “stress mindset” is closely linked to their physical and mental health: those who view stress as energising, rather than debilitating, show more adaptive physiological responses to stress and tend to perform better under pressure. Perhaps the most well-studied demonstration of mindset is its contribution to the placebo effect, with substantial evidence showing that merely believing that something will make you feel better can produce measurable physiological changes, even in the absence of an active drug. Given this surfeit of evidence showing how mindset shapes our waking lives, researchers have now begun to explore whether similar effects apply to sleep. While chronic bad sleep is linked to poor health, it has also become apparent that even one or two bad nights’ rest can make us unhappy and reduce our reaction times, impairing skills like driving. Yet we are surprisingly poor judges of how well we have slept. This even applies long term, and researchers have established that some people develop an “insomnia identity”: more than a third of those who consider themselves insomniacs are, in fact, getting decent sleep. This has led several researchers to ask whether our beliefs and expectations about sleep itself can shape how we feel. Last year, Samir Akre at the University of California, Los Angeles, and his colleagues tracked 249 people with depression for 13 weeks, taking note of both their actual sleep time using smartwatches and their self-reported sleep behaviour. The mismatch between the two sets of data was striking: many people claimed they had slept terribly, saying it had taken them a long time to get to sleep and that they had woken many times in the night. But the objective data showed that simply wasn’t true. Notably, when participants performed cognitive tests, it was the self-reported sleep quality that predicted how well they did, rather than the objective sleep metrics. In other words, the belief that they had slept badly impaired their thinking the next day more than the sleep itself. This is one of several new studies hinting that the way we think about sleep has powerful effects on our subsequent emotions and cognition. In an earlier, slightly mischievous experiment, performed in 2021, researchers allowed 16 adults to sleep for 8 hours on one day, followed by 5 hours the next. Upon waking, a secretly manipulated clock informed the participants how much they had slept. They then rated their subjective sleepiness and took part in a vigilance test that recorded their reaction times. “ When people were engaged in more positive physical activity, their sleep-quality rating tended to go up “ Those who believed they had slept 8 hours – but who had actually slept only 5 – performed significantly better on the test compared with those who had got 8 hours but thought they had been asleep for 5. Making a person believe they had slept more poorly than they did reduced their reaction times by around 20 milliseconds. This, the team says, is equivalent to the kind of deterioration in performance you would see when someone has four nights of 5 hours’ sleep or two nights with only 3 hours of sleep. The participants’ brain activity told an even more intriguing story. Slow-wave activity in the brain, called delta power, correlates with what we know as “sleep drive” – the urge to sleep. Delta power is slowest upon waking and increases throughout the day, pushing you to get some shuteye at night. As expected, delta power increased more in the daytime following the 5-hour sleep compared with the 8-hour rest. However, when participants thought they had slept longer than they did, there was a relative reduction in delta power during the day. It appears that simply believing you slept well has a powerful neurological effect, shifting your sleep drive and making you feel more alert for longer. This all suggests that changing how we think about the amount of sleep we get might help us respond better to a lack of Zs. But to fully utilise this power, we also need to consider how people judge whether they have had a good or bad night’s sleep. Nicole Tang at the University of Warwick, UK, spotted a gap in our knowledge in this department. “When you talk to people about sleep quality, everybody thinks they know exactly what they are talking about. It’s something so familiar, and yet we often have different ideas and different definitions of it,” says Tang. She noticed that, when assessing sleep, people would not only talk about the rest they had, but also about how they had felt the day before or the morning after. All too often, she says, sleep experts concentrate on the nighttime hours. “We realised we needed to stretch the timespan to look at what was happening either side of sleep, as well as what happened during the night.” Tang and her colleagues asked 100 good and bad sleepers to compare multiple sleep scenarios – with each made up of various parameters chosen at random by a computer – and choose which reflected the best night’s sleep. A typical scenario might say something like: “I did a lot yesterday, I felt positive when I went to bed. I felt moderately sleepy. My mind was blank, but I felt very comfortable lying in bed. It took me no time to fall asleep. I woke a number of times, but only very briefly. I slept for about 5.5 hours and I didn’t dream. On waking, I felt motivated to get out of bed. During the day, I felt drowsy and my head felt cloudy. My mood was bad, and I was sociable.” How we think about the way we have slept has a radical impact on how we feel It may sound a little nonsensical, but by analysing the responses given over multiple trials, the researchers could tease apart which factors were the most influential in forming our judgement of sleep quality. What they discovered was surprising: our thoughts about the quality of our sleep aren’t determined solely by what happens at night. The person’s “level of physical activity, their mood, their social ability, whether or not they can think straight” all affected judgements of sleep quality, says Tang. “ A few nights’ bad sleep doesn’t break us – unless we believe it does “ Which got Tang thinking: if what happens during the day influences perceptions of the previous night’s sleep, then perhaps a person’s feelings about their sleep changes as the day unfolds. To test this idea, she concocted a follow-up study, where 119 adults were asked to rate the quality of their previous night’s sleep every 2 hours between 8am and 10pm. They were also asked to provide information about their mood, their physical and social activity and any pain or discomfort. Finally, at the end of the day, participants took a test that asked them to remember what they had reported at the beginning of the day. More than 90 per cent of the participants changed their rating of how well they thought they had slept at least once. This wasn’t down to forgetfulness – all those who had altered their rating remembered what they had put at the start of the day. Far from being a static figure, people’s rating fluctuated as the day unfolded. What improved people’s perceptions of their sleep most strongly? Physical activity. “When people were engaged in more positive physical activity, their sleep-quality rating tended to go up,” says Tang. That held true even when they had experienced an objectively bad night’s sleep. Tang suggests that even when you have had little sleep, dragging yourself to the gym isn’t such a bad idea – it might positively reshape your memory of sleep, leading to beneficial knock-on effects. After sleeping poorly, people tend to cancel meetings, avoid exercise and think they shouldn’t go out, she says. All these thoughts are safety behaviours that put a boundary on what you do, but the research indicates this might also stop you from positively revising the way you see your sleep. A lot of people don’t realise that we are remarkably adept at coping with short-term sleep loss. “It’s a resilience we have forgotten about,” says Tang. “If your concept of sleep quality is not as rigid, if you know you can change it, then you can help yourself feel better.” Essentially, a few nights’ bad sleep doesn’t break us – unless we believe it does. How to change your perception of sleep Most of the research on s