How did you sleep last night? If you were tossing and turning in bed or staring at the clock, you'll probably feel pretty unrefreshed in the morning.
But that tired, sleepy state may not just be due to the quantity or even the quality of your sleep, as it can also be related to your way of thinking.
Because what you tell yourself the next day about how you slept and how important it is can affect your experience of fatigue.
"Everyone knows about the concept of sleep quality.
"They assume it's related to how people sleep at night, as something that can be measured," says Nicole Tang, director of the Sleep and Pain Research Laboratory at the University of Warwick, in the United Kingdom (UK).
"But what happened after sleep, as well as what happened just before going to sleep, can also have an impact."
Tang's work in this area is part of a growing body of research indicating that it's not just a night's sleep that's important for feeling rested in the morning.
It also depends on how we view sleep, our mood when we assess how tired we are, and what we are doing at that moment, Tang and her colleagues say.
The belief that our mindset directly influences our sleep is nothing new.
Decades of research largely agree that the main causes of insomnia are likely psychological processes: our sleep is disrupted when our level of arousal or excitement is elevated, which is often a consequence of our thoughts, beliefs, and the way we direct our attention.
However, many believe that they feel tired because they slept poorly - tossing and turning all night and not being able to get the quality sleep we all crave.
This phenomenon is often called "paradoxical insomnia" and has puzzled scientists for decades.
This means that people believe they slept poorly and feel tired, yet when their sleep is objectively measured, such as with polysomnography (a method of non-invasively measuring vital parameters during sleep), it turns out to be within normal limits.
This condition is probably more common than people believe, and some research suggests that it is the case for most people who suffer from insomnia.
One systematic review of studies found that this condition is present in eight to 60 percent of patients suffering from insomnia.
To be perfectly clear, insomnia and the possible associated risks are very real.
And it's no secret that if you're constantly feeling tired, you should do everything you can to improve your sleep.
But considering the impact of poor sleep experiences on how tired we feel is interesting and may offer some solutions.
At best, it can help you stay more alert without extra hours of sleep.
- Insomnia - more than a sleepless night
- "Why didn't I fall asleep again" - what are the consequences of poor quality sleep
- Insomnia and I: "I suffered for a long time"
This approach may contradict what we are often told about sleep, which is that a certain number of hours of sleep each day, without waking up, is absolutely crucial for our health.
But experts say that the exact link between sleep duration and long-term health cannot be determined, and when one is found, studies essentially highlight the connection between sleep and health, but not a necessary cause-and-effect relationship.
In other words, lack of sleep can be the cause of the problem, or it can be an underlying condition or disease that prevents someone from sleeping well - for example, people with respiratory problems often sleep poorly.
"We're problematizing our sleep," says David Samson, an evolutionary anthropologist and director of the Sleep and Human Evolution Research Laboratory at the University of Toronto, Canada.
Using objective measurement methods such as actigraphy, which tracks activity and rest cycles, Samson and other researchers found that people in hunter-gatherer societies typically sleep between 5,7 and 7,1 hours a night, which is on the lower end of the scale compared to people in industrial societies.
They also have more sleep interruptions, but that doesn't bother them either, says Samson.
Of the two groups he studied, in Namibia and Bolivia, less than three percent of foragers said they had trouble falling asleep or staying asleep, compared with up to 30 percent of respondents in industrial societies.
Neither of these two groups had a word for "insomnia" in their languages.
"When I ask them, 'Are they happy and satisfied with their sleep? Are they sleeping well?' - however you ask them this question - 9,5 out of 10 answer: 'Yes, I sleep great,'" says Samson.
"Yet we know that these foragers in these small societies sleep less than people in the economically developed world."
"In the West, people keep saying that people have never slept less."
"That's complete nonsense," he says.
Samson is one of a growing number of researchers who are pushing back against universal "rules" regarding the amount of sleep needed.
For example, researchers from the University of Oslo, the capital of Norway, recently questioned the belief that there is an "insomnia epidemic."
In an academic article, they point out that the results of laboratory studies, which have raised concerns that poor sleep negatively affects health, differ greatly from real-life findings.
"The need for sleep is dynamic in nature and has the ability to adapt to life circumstances," the researchers write.
"This means that there is no optimal amount of sleep for the same person in different situations and times."
"In fact, the need for sleep is influenced by various things, such as environment, culture, and psychological and physiological factors, which must be balanced according to the needs and possibilities of different behavioral patterns."
Anxiety in sleep
The belief that there is only one "correct" way to sleep is not only unfounded, but can also be counterproductive.
This also applies to the way we should fall asleep.
People who suffer from insomnia tend to have rigid beliefs about sleep (for example, "If I don't get seven hours of sleep, I'll feel terrible tomorrow") and are often particularly afraid of having a bad night's sleep.
They also pay more attention to sleep rules, such as watching the clock.
All of these thoughts can increase arousal and anxiety at night, making it difficult to sleep, and can also create problems the next day, Tang notes.
When people think more about how awake they were during the day, it can exacerbate their feeling that they slept poorly the night before and not only make them feel more tired, but also make them more worried about how they will sleep the next night, thus remaining in a "vicious cycle."
However, often these beliefs are not supported by facts.
People who suffer from insomnia usually think they need more sleep than they actually do and overestimate the impact of poor sleep on their daily activities.
Therefore, traditional insomnia treatment often employs cognitive-behavioral strategies that are intended to change such thoughts and reduce arousal, such as muscle relaxation exercises.
This approach could also help other people who have sleep disorders, such as parents of newborns, says Pamela Douglas, an Australian general practitioner who researches sleep and who designed the Possums sleep program for parents and children adopted by healthcare professionals around the world.
She points out that most infant sleep guidelines advise parents to monitor how much their baby sleeps and when they wake up during the night.
"Actually, we don't want to look at the clock or count the hours," she says.
Beyond the specific beliefs we have about sleep, the problem is how tightly we hold onto them, says Jason Ong, who has been researching sleep for years at Northwestern University in Illinois, United States (USA).
"The problem for people who suffer from insomnia is not just that they think, 'I need eight hours of sleep or I won't function the next day.'
"The problem is how strictly they adhere to it," he says.
His research focuses on ways to strengthen the sanctity of one's own thoughts in order to reduce adherence to such rules and beliefs.
Day after
Paying too much attention to sleep not only makes it harder to fall asleep, but can also contribute to feeling tired the next day, even if we slept well.
Ong recalls a patient who claimed he needed six hours of sleep to function the next day.
When Ong showed him the day he had logged five hours in his sleep diary, the patient said it was the night of Daylight Saving Time, but he didn't understand what had happened that night.
Only later, at the end of his workout at the gym, did he realize that he had slept for 5,5 hours, not 6,5 hours, and that's when he felt exhausted.
“I said to him, ‘Did just knowing that you slept an hour or less than usual change how you felt the rest of the day?’” says Ong.
"Does it really matter how many hours you actually slept or how many hours you think you slept?"
This could also mean that the huge increase in the use of sleep-tracking devices could backfire, warn researchers including Tang and Samson.
Let's say we wake up and feel good, but our smartwatch says we slept less than average, and then we may feel more tired than we would have if we hadn't received that information.
This is also confirmed by some research.
In one study, for example, researchers told participants who suffered from insomnia that the sleep data they were receiving was from a smartwatch.
This data was false, but the respondents did not know this.
Half were told they slept poorly, half were told they slept well.
When they reported how they were feeling later in the day, the group told they had slept poorly said they felt more tired, less alert, and were in a worse mood than the group told they had slept well.
Feeling like we slept well, even if we objectively didn't, not only affects how tired we feel, but can also affect how well we perform our daily tasks.
In a small recent study, laboratory participants woke up after either five or eight hours of sleep for two consecutive nights.
But their clocks were set to think the opposite - those who slept five hours thought they had slept eight, and vice versa.
During the test, participants who slept for five hours and thought they had slept for eight hours had faster reactions than those who were told the truth that they had slept for five hours.
Those who slept eight hours, but thought they had slept five hours, reacted more slowly than those who had actually slept eight hours and were told this.
The feeling of how we slept the night before also changes throughout the day, says Tang.
In the study she conducted, participants were asked several times throughout the day how they slept the previous night.
Even though the length of sleep the previous night was the same, their feelings changed.
While doing something they enjoyed, or during physical activity, they would suddenly have a more positive outlook on the previous night's rest.
While how we think is important, that doesn't mean we should adopt "toxic positivity," researchers warn.
"We're not trying to force people to give themselves 'false information,'" Tang says.
"But the point is that they need to understand that even if they don't sleep well one night... they can still do what they enjoy."
Tips for good sleep
So, if you have trouble sleeping, what can you do?
Experts say that all the usual advice should be followed, such as sleep hygiene, which usually includes avoiding alcohol and caffeine and going to bed at a set time.
But even so, try to adopt a less black-and-white approach to sleep.
Maybe to remember the good days you had after an imperfect sleep, or to not assume, based on some previous experience, that every day after an imperfect sleep will be bad.
Researchers, like Tang, Douglas, and Ong, also advise not to let a bad night disrupt your life too much by, for example, canceling plans for the day.
Research conducted by Tang suggests that focusing on things that lift your mood in the morning can greatly improve how you feel about how you slept.
It can also be helpful to better understand what sleep means, Tang adds.
For example, if you know that it's natural to wake up multiple times during the night, it will be less stressful for you.
"I'm not saying that sleep isn't important for overall physical and mental health," Tang says.
"But if people talk too much about how much sleep they got, they forget the fact that there are so many individual differences and many different circumstances."
"And that causes unrealistic expectations, guilt and disappointment for many."
In fact, it's probably why you feel more tired, and that can be really exhausting.
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