Expert breaks down how your body functions based on the hours of sleep you get
"If I go to sleep now, I'll get eight hours' sleep...," "okay, if I go to sleep now I'll get five hours' sleep...".
These are promises we've all made to ourselves on one night or another after being kept awake by embarrassing memories or TikTok storytimes, but now an expert has broken down exactly how your body is impacted by the hours of sleep you manage to get, whether it's the ideal eight hours, or absolutely zilch.
Of course, drifting off into dreamland at 10pm on the dot every night is a nice ideal, but in reality it's not always that easy to stick to routine. So Natalie Pennicotte-Collier, resident sleep expert at MattressNextDay, has explained that she recommends looking at sleep across the week rather than putting too much pressure on every single night.
Zero hours
A big night out, a rush of adrenaline right before bed, or stress keeping you awake - there are all sorts of reasons we can be prevented from sleeping, but Natalie has warned that 'if you go a full night without sleep, your brain is operating in a much more impaired state'.
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Even if you've not had a drop of alcohol to drink, a lack of sleep can put your brain into a similar state to being drunk.
"Reaction times slow in a way that can be comparable to being over the legal drink-drive limit, which is why regular skills like driving or even basic coordination can become risky," Natalie explained.
“Very quickly, you’ll find that your focus slips, judgement becomes less reliable, and you’re more prone to mistakes you wouldn’t normally make. At the same time, the body hasn’t had any opportunity to carry out overnight repair, so you’re starting the day already on the back foot physically and mentally."
If you're unable to sleep, you might end up feeling 'weird but tired' - a feeling which Natalie said is the result of 'your stress system stepping in to keep you alert'.
"It can mask how ‘sleep-drunk’ you actually are, which is where the danger lies," she said. "Sadly, we see this reflected in road traffic accident data.”
1-3 hours
Finally drift off at 2am, only to find yourself awake again at 4am? If that's the case, chances are you haven't managed to reach the deeper stages of sleep that our bodies rely on to actually recover day to day.
With one-three hours' sleep, Natalie said people 'can usually get through the day, but not comfortably'.
"Concentration is inconsistent, emotions feel closer to the surface, and patience wears thin much faster than usual. It’s common to feel overly reactive or overwhelmed by things that wouldn’t normally bother you," she said.
“Physiologically, the body is still under strain. Stress hormones remain elevated, energy regulation is uneven, and your immune response is reduced. You might feel ‘awake’, but your system isn’t properly supported.”
3-5 hours
As your rest becomes more extended, it's easy to think you're functioning normally, but Natalie said that's not necessarily the case.
“At three to five hours, this is where a lot of people start to believe they’re functioning normally, but brain and cognitive performance are still reduced," the expert explained. "The difference here is more subtle but persistent."
Reduced performance might be evident in the fact you're slower to process information, more forgetful, and struggling to stay engaged.
"Tasks that require sustained attention or problem-solving become noticeably harder over the course of the day," Natalie said.
“This is also where behavioral patterns start to shift, as naturally, health goal habits are very hard to stick to when you aren’t getting enough sleep. For example, you may find yourself craving high-sugar or high-carb foods more often, or not getting enough exercise.”
6-8+ hours
Finally, we make it to the ideal amount of sleep at around six to eight hours. If you're able to achieve this consistently, both the brain and body have chance to reset.
"That includes the brain’s ‘waste clean-up’ process, alongside the repair and immune support your body relies on," Natalie said.
"In my sleep clinic, I always recommend looking at sleep across the week rather than just chasing hours each night. For adults, this still means aiming for around 7.5 hours, or what I describe as five sleep cycles per night.
“This is where the body shifts out of fight-or-flight and into rest-and-digest, where real repair happens. You also get enough REM sleep, which supports memory and emotional balance, while things like stress, appetite and energy are better regulated.
“What I see in practice is that people don’t just feel more awake, they feel more focused and emotionally steady. Their thinking is clearer, their mood is more stable, and everyday tasks require less effort. You’ll also find that relationships and connections improve when you sleep better. It’s a fast, noticeable shift from just coping to feeling awake, sharp and at your best, rather than just ‘meh-functioning.’"
So, next time you're thinking you'll watch 'just one more video' before going to sleep, put your brain and body first and get to bed!
Topics: Sleep, Health, Mental Health, Science
Emily Brown