11pm: “Back from the husband’s birthday dinner and feel anxious that I need to go to bed. To soothe said anxiety, I lie in the dark scrolling through Instagram. Make mental note to paint my kitchen the same shade of pink I saw on Michelle Ogundehin’s feed. Take another 20 minutes to fall asleep thanks to a rollcall of to-dos that I didn’t do today as I was too tired.”

The impact our phones have on our sleep is extreme. When you consider that 28% of us check our devices within five minutes of lights out and 53%* of us will reach for them within 15 minutes of waking, it goes some way to explaining our poor sleep habit.

“Melatonin, the hormone that tells us we’re sleepy, is suppressed by the blue light our devices emit,” says Anna Persaud, CEO of This Works, whose best-selling product all over the world is its Deep Sleep Pillow Spray.

“Exposure to it impacts both how long we sleep for and also our readiness for sleep.” But it’s also the content of our phones. “Emails and social media can make you stressed, meaning you produce cortisol that increases your heart rate and blood pressure and suppresses melatonin, making it very hard to sleep,” says Dr Sophie Bostock, a sleep evangelist (she works with health experts and trials sleep-improvement programmes) at Big Health, the company behind digital sleep programme Sleepio.

11.40pm: “Baby wakes up. Feel like I’ve been punched in the face, get the lyrics to N*E*R*D’s new song in my head and play them on repeat.” “This earworm behaviour is remarkably common in troubled sleepers,” explains Professor Gaby Badre, neuroscientist and sleep specialist at This Works. “It’s an OCD-like phenomenon where you focus on something and become more aroused and less sleepy, and is a common sign of insomnia.”

3am: “Baby wakes up again. I think it might be broken and consider selling on eBay.”

3.15am: “Mind is dragging me from sleep as I start to mentally write this feature and grow anxious about my deadline. Feel pressure that I still haven’t launched my multi-billion-pound company. Or written my Oscar-winning screenplay. My thoughts are always totally irrational at this time.”

“The same pathways that control your emotions are very much affected cases yet for addressing our poor sleeping habits. Alongside startling anecdotes – some of the biggest human-caused disasters in the world (such as Chernobyl) were down to tiredness; someone dies every hour in a traffic accident in the US due to a fatigue-related error –by our sleep,” says Dr Bostock.

“We have seen that amygdala [responsible for the ‘flight or fight’ response] is aroused when you are short of sleep, so you become more emotional and impulsive. And your pre-frontal cortex [responsible for rational thoughts and planning] receives less glucose when you’re over-tired. In other words your ability to self-regulate goes out the window.”

Hence the 3am freakout.

5.30am: “Husband gets up for work and wakes me up. My reaction is unprintable. Seems pointless going back to sleep now, so I start scrolling Net-a-Porter for something to wear to a talk I’m hosting next week. My eyes burn, my head is pounding and I feel sick. My Fitbit Alta (from £99, fitbit.com) shows I had four hours and 22 minutes of very interrupted sleep and my heart rate – which it also tracks – indicates I never entered deep sleep.”

6am: “I used to spend money on handbags, now I spend it on coffee beans. I make myself a two-shot flat white followed by a Diet Coke. This will be followed by at least three more Diet Cokes and another coffee.”

“People reach for caffeine because they know it keeps us awake,” says Walker. “Caffeine’s a psychoactive stimulant, the only one we readily give our children, and it’s the second most-traded commodity on the planet, which should tell you all you need to know about sleep deprivation. The danger is that even if drinking caffeine doesn’t stop you going to sleep, when it’s in the brain at night you don’t fall into as deep a sleep, meaning you don’t wake up feeling refreshed. Caffeine has an average half-life of 5-7 hours, meaning if you drink a coffee with dinner at 7.30pm, 50% of that may still be active and circulating through your brain tissue at 1.30am. Simply do not drink caffeine after midday.” Instead of a latte, drink lots of fluids – even mild dehydration can lead to fatigue – or opt for green tea, which has around a third of the caffeine of an Americano but is shown to keep energy levels up for 3-6 hours. Tea also contains the amino acid theanine, which may improve attention and alertness.

9am: “Around 3.30am last night, I resolved to go vegan and become a ‘yoga person’. I make some Bircher muesli with bee pollen (only £7) and chia seeds. I think the muesli is laughing at me. Ten minutes later I have white toast and Marmite because I’m so tired ‘I deserve it’. Today feels like another write-off, diet-wise, and I know I’ll eat white carbs and sugar for the rest of the day.”

“Our appetite hormones are markedly affected by poor sleep,” explains Walker. “Leptin is a hormone that signals you are full while ghrelin tells your brain you’re hungry. When people experience just one week of short sleep, leptin levels drop so you don’t experience the satiety you typically would and ghrelin increases meaning you eat more. Typically, those who ‘undersleep’ consume an additional 250-500 calories a day.”

Research has also found that lack of sleep alters the part of the brain that influences impulse control, so while we may intend to eat well, when the doughnuts come out we instinctively reach for one. Sugar and white carbs give us an energy rush followed by a slump, so we should be looking for a breakfast with protein and slow-release carbs – poached eggs on wholemeal toast or oats with chia seeds. The other trick is to eat small portions regularly throughout the day.

11am: “Take fistful of Maltesers from the fridge. And a cookie. And Kit Kat. Stop judging.”

1pm: “Meet editor for working lunch. I have a hundred ideas at the minute, but what I don’t have is the energy to see them through. I feel caught in a vicious cycle of putting things off until I get more sleep, but then doing nothing to ensure I actually get more sleep.”

We’re so used to the rhetoric that successful people wake at 4am to check their emails and do their work that somehow not sleeping has become a badge of honour. “But research shows that lack of sleep makes us less productive,” says Professor Walker.

Losing sleep reduces the ability to concentrate and problem-solve. ‘Under-slept’ employees exert less effort when in groups and opt for less-challenging problems. The more or less sleep a leader has, the more or less charismatic they appear to employees.”

The minimum sleep needed to remain productive varies from person to person – some studies say it’s hereditary –but Badre explains what is crucial is to get three hours of continuous sleep in order to experience one cycle of deep sleep – where cells can regenerate – and one of dream sleep.

3pm: “Feel like I’m at a rave thanks to a racing heart and overall sense of jitteriness, but I’m actually on the Victoria Line. Get off a stop early and walk home. People are always surprised when I tell them how little I sleep because I pack a lot in, but despite my tiredness I do still have lots of energy.”

“You are hypermanic,” explains Badre. “When you sleep your cortisol levels decrease; they rise again just before you wake up. If you’re not sleeping enough, your body will accumulate too much cortisol and you become hypermanic. Many people try to burn it off with high levels of activity, but after a certain level you burn out.”

4pm: “On the advice of the various sleep experts, I’ve taken tests to see the impact of my lack of sleep. One thing dramatically impaired is reaction time – hence why many traffic accidents are caused by fatigue. Typically, you should be most alert between 2-12 hours after waking, so I take a reaction test (take a look at healthysleep.med.harvard.edu for a similar one) at intervals throughout the day. By 6pm, when I’m often driving, my reaction time is considered dangerous. This scares me.

I also do an adrenal stress profile, which measures cortisol and melatonin levels throughout the day (try medichecks.com). As mentioned, excess cortisol is extremely detrimental to sleep and behaviour. It’s no surprise that I have abnormal spikes in mine all day. Vitamins C, B5 and zinc have all been shown to decrease cortisol levels.”

6pm: “I used to consider myself competent, but today I forgot to pay a deposit for a hen do, sendback Zara boots, and the name of every single new person I’ve met in the last 10 years.”

“Poor sleep affects our memory in two ways,” explains Walker. “Firstly, you need sleep after learning to hit the ‘save’ button on new memories so you don’t forget. But you also need it before learning. Without it, memory circuits in the brain become waterlogged and you can’t absorb new information. Most worryingly, we know that people who report getting insufficient sleep across their lifetime are at a far higher risk and probability of getting Alzheimer’s.”

8pm: “Time to tackle my face. It looks a bit like the Scream mask. The effect of sleep deprivation on my body seems to be grey skin, eyebags and hair like brittle candy floss.”

“Sleep is absolutely necessary for optimum skin health,” explains Dr Michael Pugliese, CEO of Circadia. “During the day our metabolic function is at a much higher rate than during sleep. At the same time, the body is producing the required energy it needs to get us through our daily activities, it also makes free radicals naturally as part of the process. The more activity without rest, the more free radicals will be made, creating wear and tear on the skin. Dark circles and puffy eyes are linked to inflammation and an impaired vascular system exacerbated through lack of sleep.”

While drinking lots of water can help flush out some toxins, Dr Pugliese recommends looking for products that have great emollient and humectant profiles, such as Dr Pugliese Nighttime Repair Plus.

9pm: “Go to bed. Start reading Little Fires Everywhere by Celeste Ng and it’s so good I don’t even pretend I’m going to get an early night. I’m a sleep failure.”

In conclusion: I’m a mess. This experiment has taught me that we need to completely change the way we think about sleep.

“Sleep is the most effective thing you can do to reset your brain and body,” stresses Walker. “The shorter you sleep, the shorter your life.”

Existing on a few hours sleep doesn’t make you a superwoman, it makes you less capable at your job and less happy in general. And feeling like the walking dead is indicative of the impact that a lack of sleep is having on your body. There are many, many reasons why we don’t sleep (see the previous page for the most common, and advice on how to tackle them), so there is no ‘one size fits all’ prescription to get the magic eight hours.

For me, it means leaving my phone outside of my bedroom and admitting there are things in life I have to forfeit in order to sleep; for you it may be a CBT programme (try sleepio.com) or reducing how much you drink (experts consider alcohol to be a huge sleep enemy).

But the takeaway here is that prioritising sleep above work, exercise, Instagram or a night of whisky cocktails is probably the best thing you can do for your health. On that note, I’m off to bed.

Sleep deprivation: This is how lack of sleep is really affecting our health