Jessica Lindsay
Published December 3, 2025 3:00am
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Quality sleep is vital for health (Picture: Getty Images)
After a sleepless night, you’ll feel slow, sluggish, and wish you were back in bed – but until you finally get there, your body is working overtime to keep you going.
The impact of a single night without shut-eye pale in comparison to chronic insomnia, which can lead to a weakened immune system, mental health issues, menstrual irregularities and an increased risk of heart attack and stroke.
Still, according to the experts, any amount of missed sleep has the potential to start a ‘ripple effect’ of physiological responses, increasing in severity the longer you’re awake.
One study found that staying up for 24 hours is akin to drinking four glasses of wine or beer, while sleep deprived teenagers eat 210 more calories the next day for every hour of rest lost.
Dr David Garley, director at The Better Sleep Clinic tells Metro that the way your body reacts to sleeplessness throughout the day depends on your chronotype – aka when you tend to be most alert and productive – and ‘a night owl would feel this more in the morning, whereas a lark might feel it more in the evening.’
Assuming you stick to the ‘standard’ 9-5 schedule though, here’s what goes on behind the scenes when you don’t get any sleep the night before.
One night isn’t the end of the world, but you will likely struggle the next day (Picture: Getty Images)
First thing in the morning
When your alarm goes off after a night spent staring at the ceiling, Dr Hana Patel, NHS GP and resident sleep expert at Time4Sleep says ‘you’ll likely feel immediately unrefreshed.’
‘Despite being exhausted, you might also feel a little jittery or stimulated as your body tries to force you into wakefulness,’ she tells Metro.
‘Sleep deprivation can also impact your appearance, so you might have more hanging eyelids, red and swollen eyes, dark circles and wrinkles around the eyes, or droopier corners of the mouth.’
According to Dr Garley, ‘blunted’ cognition and an ’emotionally slightly friable’ feeling tends to be worse for night owls in those first few hours of the day.
One hour into your day
‘One hour after your usual wake time, your cortisol levels will rise sharply as the body interprets lack of sleep as a threat to stability, giving you a temporary sensation of alertness driven by stress,’ explains Dr Patel.
‘Cortisol – also known as the “stress hormone” – normally peaks an hour after waking up no matter the quality of your sleep, but this is typically worsened by bad sleep. Elevated cortisol is linked to heightened anxiety and reduced immune function, and can even lead to insomnia if it persists.’
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Mid-morning
At this point, Dr Garley says many are comfortably into the day phase of the circadian rhythm, which can support function despite poor sleep, commenting: ‘Mood and cognition can improve, along with energy levels.’
That said, others may find the opposite is true, instead experiencing reduced focus levels and memory, problem-solving, and emotional capabilities.
‘This is because cognitive functions are impaired after a sleepless night, causing you to experience brain fog,’ says Dr Patel. ‘Due to low energy, your physical strength and energy levels will typically be lower too, with a slower reaction time.’
Lunchtime
‘Poor sleep affects the hormones leptin and ghrelin, and this works to increase your appetite,’ says Dr Garley. ‘This might mean you have a bigger lunch, perhaps more carb craving.’
However, he adds that it’s important to resist your most ravenousness impulses, as the natural midday dip in most people’s circadian rhythmsdoesn’t pair well with a carb-heavy meal, and ‘could make for some quite significant drowsiness.’
What do to after a bad night’s sleep
Dr Ravi Lukha, medical director at Bupa UK Insurance, offers his advice on how to approach the day after a sleepless night.
Step away from excess caffeine
‘Don’t load up too much on caffeine throughout the day, regardless of how tired you feel,’ Dr Lukha tells Metro. ‘If you are taking on caffeine, space it out and try to avoid drinking it after midday, as that can affect sleep that evening.’
Fuel yourself wisely
The doctor explains: ‘When your blood sugar regulation is fluctuating more than usual, it’s common to crave stodgy, sugary foods. Try to opt for food that can help reduce fatigue, instead.
‘Fruit, vegetables, wholegrains and foods containing lots of omega-3 fatty acids – like fish, seeds and nuts – may help give you a healthier boost and avoid consuming excess sugar that could leave you feeling crashed out.’
Introduce movement
While a workout probably feels like the last thing you fancy when your shattered, Dr Lukha says ‘it can actually help bring your circadian rhythm back into regularity.’
He recommends a walk or run outside, as ‘sunlight sends signals to your brain to tell you that you should be awake.’
Be nap savvy
‘Napping has been proven to help you feel less sleepy, less grumpy and less forgetful – but only under the right conditions,’ adds Dr Lukha. ‘This means only napping for between 10 and 20 minutes.’
Mid-afternoon
As the day continues and the circadian rhythm slump is over, Dr Garley says you may ‘get a second wind’, with your mood, productivity and energy picking up.
But as Dr Patel also notes, at the five to eight-hour mark after you’d normally have woken up, you might go through episodes of ‘miscrosleep’, which is an involuntary and very brief intrusion of sleep. And while this usually only lasting a few seconds, it can be especially dangerous if you’re driving or using heavy machinery.
‘Sleep deprivation can also affect your emotional state, leaving you more irritable, impatient, depressed, or anxious,’ she continues. ‘The amygdala, responsible for processing emotions, becomes more reactive after a sleepless night, so smaller stressors feel bigger, often leaving people overwhelmed and more sensitive than usual.’
The rest of the day
Dr Patel says: ‘As fatigue accumulates into the afternoon and evening, motivation and concentration generally decline further. It can be tempting to try to nap to combat the tiredness; however, this can be counter productive and can impact your ability to sleep well when you do go to bed.’
Rather than napping, he recommends waiting until your regular bedtime so you can recover your normal sleep cycle, as well as trying to avoid processed or salty foods, as these can cause you to feel more fatigued.
Try to resist the urge to nap (Picture: Getty Images)
This evening decline is probably more likely for morning larks, says Dr Garley, whereas night owls ‘might start feeling themselves a bit more’.
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Either way, he highlights the importance of not putting things in the spotlight too much, as this ‘can lead to higher amounts of stress and worry than might be justified.’
Dr Garley continues: ‘This worry can actually be what disrupts your sleep further, and lead to more consistent problems with sleep.
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‘The best thing you can do when sleep deprived is to be kind to yourself, try to keep your day as typical as you can, and avoid the urge to go to bed too early the following night, as this can sometimes throw off your natural rhythm.’
Ongoing sleep loss
Although the odd night of tossing and turning is unlikely to have much long-term effect, Dr Patel says that it’s vital to address sustained sleep deprivation.
‘Studies suggest that long-term sleep disruption and chronic lack of sleep can be risk factors for certain neurodegenerative disorders like Alzheimer’s Disease, and make it harder for the body to process sugar, increasing the risk of type 2 diabetes,’ she explains.
‘Poor sleep can also cause short term weight fluctuations. This is because chronic lack of sleep can decrease our motivation to exercise and increase our stress levels, and potentially lead to a bigger appetite.’
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