The more you put off 'enjoyment,' the more your sleep is disrupted—the deep connection between pleasure and sleep as shown by neuroscience
'I'm tired today, so I'll leave the things I like for tomorrow.'
How many times have you said those words?
In the daily grind of balancing parenting and running a business, 'enjoying yourself' often gets pushed to the back burner. After I finish what I need to do. After I have some breathing room. After things settle down a bit—but that moment never comes.
And then, even when night comes, you can't sleep. You're exhausted, but your brain won't stop.
In fact, this is deeply connected to putting off 'enjoyment.' It's not about willpower or your mindset; it's a matter involving hormones and the nervous system in your brain. Today, I will explain that mechanism as clearly as possible, while still going into depth.
◎ The true nature of 'I'm tired, but for some reason, I can't sleep'
☆ Fatigue and sleep are actually different things
Do you think that if you're tired, you'll be able to sleep? In reality, fatigue and sleepiness operate on different systems.
You feel tired mainly because a substance called 'adenosine' accumulates in your brain. Adenosine builds up the entire time you are awake, and once it exceeds a certain amount, you get the sensation of being 'sleepy.' By the way, caffeine works by temporarily blocking the receptors for this adenosine to wake you up.
However, to actually 'fall asleep,' other conditions must be met. Your parasympathetic nervous system must be dominant. Your stress hormone (cortisol) must be low. Your sleep hormone (melatonin) must be released.
Cortisol has a natural rhythm: it is high in the morning and gradually decreases toward the night. This is called the 'circadian rhythm.' When this rhythm is balanced, your body's cycle functions so that you naturally feel sleepy at night and wake up refreshed in the morning.
However, a sense of obligation like 'I have to do this' or chronic stress disrupts this cortisol rhythm. When the brain determines there is a 'threat,' it continues to secrete cortisol even at night. No matter how 'sleepy' you feel, if cortisol remains high, the brain judges that it is 'still in combat' and cannot enter deep sleep.
A night where you 'are tired but cannot sleep' is a sign that something other than fatigue is happening.
☆ 'Lack of enjoyment' keeps the brain's wakefulness switch pressed
What is happening inside your brain at the end of a day where you put off 'enjoyment'?
If you spend the whole day running on 'I have to do this' and go to bed without having experienced anything happy or fun, your brain's reward system is in a state of 'I haven't gained anything today.' The brain continues to send signals that 'the expected reward was not obtained,' feels that 'something is still missing,' and tries to keep you awake.
Furthermore, the sense of obligation to 'do something' keeps cortisol flowing. Cortisol is a hormone that sends signals to 'wake up, fight, and stay alert.' Even if you go to bed while this is high, your brain judges that it is 'still in combat' and cannot enter deep sleep.
'Lack of enjoyment' keeps the brain's wakefulness switch pressed—this is one of the causes of sleepless nights.
◎ Three mechanisms by which not enjoying yourself disrupts sleep
☆① Dopamine deficiency—'I'm not satisfied yet today' hinders sleep
Dopamine is a neurotransmitter released when you achieve something, do something you like, or feel happy. When enough dopamine is released during the day, your brain feels 'that's enough for today' by night, and your alertness naturally settles down.
What is interesting here is that dopamine includes not only the 'joy of attainment' but also the 'joy of anticipation.' Just thinking 'I have plans to do something I like tonight' starts the release of dopamine. In other words, incorporating 'enjoyment' into your day is also a form of preparation for sleep.
However, on days when you have had almost no experiences of 'enjoyment' or 'happiness,' your brain's reward system continues to send signals that you are 'not yet satisfied.' Even when you try to sleep, the feeling that 'something is missing' gets in the way, making it difficult to drift off easily.
What is even more troublesome is the vicious cycle. According to research by Volkow et al. at the University of Pennsylvania (2012, Journal of Neuroscience), it has been reported that 24 hours of sleep deprivation reduces the sensitivity of dopamine receptors in the brain. This is a state where dopamine is being produced, but the brain becomes 'less able to feel it.' Not enjoying yourself disrupts your sleep, and disrupted sleep makes it harder to enjoy yourself—this spiral is scientifically proven by neuroscience.
☆② Excess cortisol—a sense of duty keeps 'combat mode' active
Cortisol has a natural rhythm of being high in the morning and decreasing toward the night. However, the important point here is why it doesn't decrease.
Cortisol tries to maintain a high level as long as the brain judges that it is 'feeling a threat.' That 'threat' is not limited to external enemies or dangers. Thoughts like 'I won't make the deadline,' 'that matter hasn't been resolved yet,' or 'I need to do better' are also significant 'threat signals' to the brain.
If you spend your day filled with a sense of duty to 'have to do this,' your brain stays in 'threat mode' the whole time. Even at night, it continues to release cortisol, thinking 'there are still unresolved problems,' and your sleep becomes shallow. You are more likely to have frequent dreams, wake up in the middle of the night, or have mornings where you 'don't feel like you slept.'
On the other hand, research shows that laughter, joy, and enjoyment effectively lower cortisol. In a meta-analysis published in 2023 (Kramer CK & Leitao CB, 2023, PLOS ONE), which analyzed 8 studies and 315 people,it was reported that laughter interventions reduced cortisol by an average of 31.9%, and even a single laughter session reduced it by 36.7%.
What this means is that the moment the brain judges 'it is safe now, I am enjoying myself,' cortisol drops dramatically. 'I sleep well on nights when I have enjoyed myself' is not just in your head; it is the result of this mechanism.
☆③ Serotonin depletion—daytime emotions determine nighttime sleep
Melatonin is known as the 'sleep hormone.' In fact, the raw material for this melatonin is serotonin. Serotonin secreted from the raphe nuclei during the day is converted into melatonin at night through an enzymatic reaction in the pineal gland (Source: Hardeland R, 2009, Cell and Tissue Research).
In other words, on days when enough serotonin is produced during the day, plenty of melatonin is released at night, making it easier for natural sleepiness to arrive. Conversely, if there is little serotonin during the day, there is also less melatonin at night, and sleep becomes shallow.
Serotonin is called the 'happiness hormone' because its secretion is promoted when your mood is stable, when you are enjoying yourself calmly, and when your heart is satisfied. Conversely, if a daily life of duty, stress, and lack of joy continues, serotonin secretion decreases.
There is another interesting fact. About 90% of the serotonin in the body is produced not in the brain, but in the gut. And the function of the gut is deeply linked to the autonomic nervous system. If the sympathetic nervous system remains dominant due to a sense of duty or stress, gut function can be disrupted, which may affect serotonin production.
When serotonin decreases → melatonin also decreases → natural sleepiness is less likely to arrive → sleep becomes shallow.
'How much you enjoyed yourself during the day' determines the amount of melatonin at night.The more you put off enjoyment, the shallower your sleep at night becomes—this is the simplest mechanism.
◎ The neuroscientific basis for how 'enjoyment' improves sleep
☆ Research showing that laughter reduces cortisol by over 30%
Let's take a closer look at the study by Kramer & Leitao (2023, PLOS ONE) mentioned earlier.
This study is a meta-analysis of eight randomized controlled trials that examined how 'laughter' affects the body's stress markers. After looking at data from 315 people, it was found that cortisol levels dropped by an average of 31.9% following laughter interventions. Furthermore, even a single laughter session resulted in a 36.7% decrease, which is quite an impressive figure.
Even if you don't do it every day, just enjoying yourself and laughing a little today can significantly reset the cortisol that interferes with your sleep. The saying 'laughter is the best medicine' is properly backed by data.
What is important here is the quality of the 'laughter.' Forced laughter or obligatory smiles do not lower cortisol much. The research focuses on 'spontaneous laughter.'The moment you laugh because something is genuinely funny, without any sense of obligation—that is what lowers cortisol most effectively.That is why it is important to 'enjoy and laugh.'
☆ Positive experiences enrich non-REM sleep
In January 2025, a research group including members from RIKEN and Kobe University announced interesting findings regarding the relationship between positive emotional experiences and sleep (Neuron, January 29, 2025).
According to the study, it was found that during non-REM sleep (deep sleep) following a positive experience (reward experience), the coordination of neural activity between the amygdala, which processes emotions, and the cerebral cortex increases. This coordination is thought to play an important role in the integration of emotions and memories.
To put it more simply, the more days you have where you experience things that make you happy or joyful, the more likely it is that your brain can organize information more effectively while you sleep. Rather than going to sleep with negative emotions lingering, falling asleep with positive emotions might make the brain's nighttime work more 'enriched.' This is the background behind why you often feel refreshed the morning after a day you enjoyed.
☆ 'Time for enjoyment' activates the brain's organization mode
The Default Mode Network (DMN) is a neural network that becomes active when the brain is daydreaming, enjoying itself, or taking a walk. It uses 60–80% of the brain's total energy and is actually a very important circuit responsible for organizing information, consolidating memories, and generating ideas.
The phenomenon of 'getting good ideas in the bath' or 'suddenly finding an answer while walking' is precisely the result of this DMN being active. Creative processing is happening deep in the brain when you are not consciously thinking about it.
'Time for enjoyment' is the time when this DMN is active. If you keep running on nothing but a sense of obligation, your brain never gets the chance to enter DMN mode, and information piles up without being organized. The feeling of having a 'heavy head' or 'not being able to think of anything' may be a sign that your DMN is not functioning.
By enjoying yourself and letting the DMN work, your brain gets organized, and the waste removal system during sleep (the glymphatic system) also begins to function more efficiently. Enjoyment is also a 'warm-up exercise' for sleep.
◎ What happens when 'postponing enjoyment' becomes chronic?
☆ Sleep debt and pleasure debt accumulate simultaneously
When 'postponing enjoyment' becomes a habit, two types of 'debt' accumulate at the same time.
One is sleep debt—the accumulation of a little bit of lost sleep every day. The other is pleasure debt—the accumulation of a lack of emotional experiences of 'happiness and joy.'
These two are linked.Pleasure debt accumulates → serotonin and dopamine become insufficient → sleep quality drops → sleep debt increases → the brain becomes exhausted → you become even less able to enjoy things → pleasure debt increases again.
Research shows that sleep debt is not easily resolved by catching up on sleep on the weekend (Source: Cappuccio FP et al., 2010, Sleep). Similarly, pleasure debt is not easily resolved by 'having a big fun time once in a while.' It is important to replenish it little by little, every day.
When this cycle becomes chronic, it affects the entire body, leading to decreased judgment, emotional instability, and lowered immunity. Accumulating small pleasures every day is actually the most efficient preventive measure.
☆ 'No longer being able to enjoy things' is not laziness, but brain exhaustion
If you start feeling like, 'Lately, I don't enjoy the things I used to like' or 'I just don't feel motivated,' it might not be that you are slacking off, but a sign that your brain is exhausted.
In psychiatry, this state is called 'anhedonia' (loss of pleasure). You can no longer enjoy things you used to enjoy. You find it harder to feel interest or joy. While this is one of the symptoms of depression, it is also a state that easily occurs due to chronic sleep deprivation and a lack of enjoyment.
As shown by research from the University of Pennsylvania (Volkow et al., 2012), when sleep deprivation continues, the sensitivity of dopamine receptors drops, making it harder to feel 'joy' even when doing the same things. This is a physiological change in the brain, not a matter of personality or willpower.
To break out of a state of anhedonia, you don't need to look for 'big pleasures.'Start by carefully gathering those subtle sensations of 'I might like this a little.' The accumulation of small 'happy' moments will gradually restore the sensitivity of your dopamine receptors.
☆ Why parenting business owners are particularly prone to this
Business owners and entrepreneurs who are raising children have a structure that makes them prone to falling into this vicious cycle.
Taking care of children, housework, work, staff matters, management decisions—they spend all day moving for 'someone else' or 'the organization.' Added to this is the guilt of 'Is it okay for me to be the only one having fun?', causing enjoyment to be pushed further and further back.
Furthermore, sleep is often fragmented during child-rearing. Night crying, waking up early, staying up late—in addition to an environment where sleep quality easily drops, if you also cannot take time for enjoyment, the speed at which the double debt accumulates increases.
There is also the problem of 'not realizing you aren't enjoying yourself.' In the midst of busyness, your senses become dull, and you may reach a state where, if asked, 'By the way, when was the last time you felt purely happy?', you cannot remember. This is a sign of chronic pleasure debt.
◎ The concept of 'scheduling enjoyment first'
☆ 5 minutes of 'zero-obligation time' a day changes your sleep
'Enjoyment' is not something you engage in later; it is something you schedule first.
Try to intentionally create '5 minutes of zero-obligation time' somewhere in your day. If you say 'I'll do it if I have time,' it will inevitably disappear. It could be 2 minutes spent slowly drinking your morning coffee. It could be 10 minutes spent cooking while listening to one of your favorite songs. It could be the time you spend watching one favorite video after your children have gone to sleep.
The important thing is that there is 'zero sense of obligation.' It is not for the sake of 'health' or 'productivity,' but a pure time spent 'just because I like it.' This time replenishes serotonin and dopamine, lowers cortisol, and builds the foundation for your sleep at night.
Why is even 5 minutes effective? It is because the brain processes 'happy experiences' as 'important information.' The brain prioritizes memories associated with emotions. Even if it is only 5 minutes, 5 minutes of pure enjoyment is etched into your memory as 'I had a fun time today.' And that memory becomes the material that lowers cortisol in your brain before you sleep.
☆ Say one thing you were 'happy about' out loud before going to sleep
Before you go to sleep, try saying just one thing you were 'happy about or enjoyed' today out loud.
It is known that putting emotions into words activates the prefrontal cortex and calms the activity of the amygdala, which continues to process emotions excessively (Source: Lieberman MD et al., 2007, Psychological Science). Just by saying 'I was happy' out loud, dopamine is re-secreted, cortisol drops, and the parasympathetic nervous system becomes dominant.
The point is to 'say it out loud.' It has a stronger effect on the brain than just thinking about it in your head. This is also related to a phenomenon called the 'self-reference effect,' where words you speak yourself are processed by the brain as 'more important information.'
The brain right before falling asleep is in a theta wave state, which is the time when access to the subconscious is most open. By placing the emotion of 'I enjoyed today too' into that 'golden window,' that feeling is gradually etched into your subconscious.
☆ Why the 'happy-go-lucky' way of life is the ultimate sleep habit
Seeking out what makes you happy and not putting off what you enjoy—the happy-go-lucky way of life is the ultimate sleep habit from a neuroscience perspective.
By accumulating 'happiness and enjoyment' throughout the day, serotonin is continuously secreted, becoming the material for melatonin at night. Dopamine is replenished, allowing you to sleep with the feeling of 'I am satisfied today.' Cortisol drops, making it easier to enter deep non-REM sleep.
It is not 'enjoying for the sake of sleep,' but rather, if you live a happy-go-lucky life, your sleep will naturally fall into place—I believe this chain reaction is the most effortless and sustainable form of sleep improvement.
'Enjoying yourself is not an escape,' 'Enjoying yourself is healing yourself,' 'Enjoying yourself is the ultimate self-care'—this is not just a mental theory, but a neuroscientific fact.
Summary: If you want to sleep well tonight, enjoy yourself today
'Enjoyment' and 'sleep' are deeply connected from the perspective of neuroscience.
When you do not enjoy yourself, dopamine levels drop, and your brain tries to stay awake, signaling that it is 'not yet satisfied.' Continuing to run on a sense of duty keeps cortisol levels high, which interferes with deep sleep. A lack of joy and fun leads to a depletion of serotonin, making it difficult for the body to produce melatonin.
Conversely, on days when you enjoy yourself, cortisol levels drop (Kramer & Leitao, 2023, PLOS ONE), positive experiences enrich non-REM sleep (RIKEN/Kobe University, 2025, Neuron), and serotonin is converted into melatonin at night.
Three things you can try starting tonight:
- Say one thing out loud that made you happy or was fun today (before going to bed)
- Schedule '5 minutes of zero obligation' somewhere in your day tomorrow
- Let go of the belief that 'it is okay to put enjoyment on the back burner'
On nights when you have scheduled enjoyment in advance, you will naturally sleep more deeply. The feeling that 'today was fun' deepens tonight's sleep. 'Enjoyment' is the ultimate investment in sleep.
■ Main References
Kramer CK, Leitao CB. Laughter as medicine: A systematic review and meta-analysis of interventional studies evaluating the impact of spontaneous laughter on cortisol levels. PLOS ONE. 2023;18(5):e0286260.
Volkow ND, et al. Evidence that sleep deprivation downregulates dopamine D2R in ventral striatum in the human brain. Journal of Neuroscience. 2012;32(19):6711-6717.
Hardeland R. Melatonin: signaling mechanisms of a pleiotropic agent. Cell and Tissue Research. 2009;347(3):665-676.
Cappuccio FP, et al. Sleep duration and all-cause mortality: a systematic review and meta-analysis of prospective studies. Sleep. 2010;33(5):585-592.
Lieberman MD, et al. Putting feelings into words: affect labeling disrupts amygdala activity in response to affective stimuli. Psychological Science. 2007;18(5):421-428.
RIKEN/Kobe University Press Release, 'Neural mechanism elucidating how emotions strengthen memory,' January 30, 2025.