It's four in the morning, as the Leonard Cohen song goes. But I'm not in New York. I'm in Tesco. And I can buy a giant flatscreen TV, a washing machine, a mountain bike or a block of cheese. You drive through a dark sleeping Dublin to get to the hulking ship that is Clare Hall on the Malahide Road. Being the only customer in a giant supermarket is pretty lonely. It's much more Night of the Living Dead than Night at the Museum . The glass and steel complex is near-empty. There's an army of staff packing shelves surrounded by products and wrapping. A chirrupy siren competes with the piped happy pop music.The hanging sign advertising Tesco insurance sways in a ghostly draft. I buy blueberries when what I actually needed was bread.

An Irish Rail worker comes out carrying milk, bread and a bag of sugar in his arms. He’s been a night worker for 15 years. When his wife goes to work, he loves the peace and quiet and he’ll potter round the house for a while, “see the sunlight”. Almost all his friends work nights. What’s it like living in this night world? “There’s less traffic, less everything,” he says cheerfully.

Another shopper, taxi driver Alan Dunne, has just finished his shift and is heading home to bed with three plastic bags of groceries. He'll sleep until around 1pm, he says. He's been on nights for 11 years. John Roche is a delivery driver and merchandiser for a Drogheda egg supplier and he's coming to check on displays. He'll typically go to bed at 9pm or earlier in order to get up for a 4am start. "I'm a big fan of sleep," he says by way of explanation.

Just over half a century ago, America’s first 24-hour store opened in Austin Texas. Three years earlier, in 1959, the phrase “circadian rhythm” was coined from the Latin for “about a day” to describe the natural human waking and sleeping cycle. Sleep is one of the last mysteries of being human. We spend a third of our lives doing it, and theories about why have shifted as sleep scientists make more discoveries. It’s 134 years since Edison invented the light bulb and the means for a wide-awake 24-7 world. And yet, our stubbornly unevolved bodies still need a minimum of five hours sleep in every 24 hours.

But are we getting enough? An average of one in 10 of us suffers from insomnia and figures show a dramatic jump in the numbers of people in Ireland who are struggling to get a good night’s sleep. In the six years between 2005 and 2011 prescriptions for sleeping pills for medical card holders have doubled. In 2005 over 545,000 sleeping tablet prescriptions were written under the the medical card scheme. In 2011 the figure was over a million, making sleeping tablets like Zimovane and Ambien more commonly prescribed than antibiotics. (This is only partly explained by a 47 per cent increase in the number of medical card holders in the same six-year period.) A further 180,000 prescriptions for sleeping pills were written under the drug reimbursement scheme in 2011. The figures for private GPs prescribing sleeping pills could be seeing similar increases but these are not recorded by the HSE.

The last Irish sleep study by Amarach research in 2010 found that one-third of adults felt in some way sleep deprived and that people getting the least sleep were “three times as likely to say the economic situation in Ireland is bad and getting worse as those getting the most sleep.”

Whether a bleaker economic view leads to insomnia (as we lie awake worrying about mortgage debt) or the insomnia leads to the bleaker economic view is an interesting question. Last month, in research for the Road Safety Authority, 14 per cent of Irish adults told Amarach researchers that they had nodded off while driving. Add in the fact that 20 per cent of the nation are shift workers and it seems a good night's sleep is eluding an awful lot of us these days.

At a more civilised daytime hour over coffee in NUI Maynooth psychologist and circadian rhythm expert Dr Andrew Coogan explains why sleep matters. "I think sleep is now viewed as a core pillar of health along with exercise and diet," he says.

There are two big ideas behind why we sleep. The first is that it helps our brains to work better, Coogan says. “Sleep consolidates memory, the brain replays what it’s taken in during the day, and that process strengthens synapses that form memories.” In studies, people who are allowed to sleep between memory tasks remember 15 per cent more than those who haven’t had some shut-eye. The second idea is that sleep helps our bodies to restore, regenerate and regulate everything from our appetite and our immune systems to our cardiovascular health.

Sleep is often the first thing to break down when something goes wrong with our bodies or minds. “In the case of Alzheimer’s, a disturbed sleep happens long before the onset of dementia,” Coogan says. Studies following people over decades have found that sleep disruption happens before the onset of numerous diseases.

Not all sleep is the same, which explains why someone getting eight hours might still wake feeling exhausted. We typically drift off into a light non-REM (Rapid Eye Movement) sleep which deepens into slow-wave sleep. “Slow-wave sleep is restorative. It makes us feel refreshed and better,” Coogan explains. “REM sleep is classically associated with dreaming. Brain activity in REM sleep looks very similar to brain activity when we’re awake.” On a typical night, a person will go through several 90-minute cycles of slow-wave to REM sleep and back. “You’re more likely to remember a dream if you wake up in an REM episode. Slow-wave erases the memory of the dream. It’s important that you progress through the cycle correctly.”

Phone-app alarms claim to monitor your breathing or movements and wake you only from an REM sleep rather than a slow-wave episode. In the US, a headband called the Zeo will send data to your phone calculating your cycles of sleep. Coogan gets a kick out of reading the comment section on the site where customers get competitive about how the number of minutes of slow-wave sleep they’ve racked up.

Some types of sleep are better than others. “Alcohol affects sleep. It’s a somnolent so it puts you to sleep, but it affects the sleep cycling, which explains why people who’ve drunk a lot can sleep for 12 hours but wake up and still feel terrible.”

If you need an alarm clock to wake up on a work day, you might be suffering from what Coogan describes as “social jet lag”. A lie-in on a day off can shift you into a different time zone. Back in the world of work, your body is still in the weekend time zone. If we’re sleeping within a consistent range, we shouldn’t need alarm clocks.

As any parent knows, small children wake early. In the teenage years, that shifts to long lie-ins. “Teenage sleep patterns are completely at odds with early school starts,” Coogan says. “In studies where the school day shifts to a later start, teenagers do better.” As we age, we begin to wake early again. “In old age, there can be an extreme shift to early waking at four or 5am. It can contribute to social isolation, because you’re now out of sync with the rest of the world.”

There are some basic indicators of how wide awake Ireland is at night. Eirgrid’s 24-hour graph of electricity demand has a circadian rhythm of its own. From midnight the demand drops, as lights, TVs, computers and cookers are turned off and most households go to sleep. The bottom of the curve happens between 4am and 4.45am, and then demand begins to climb again. On an average night, the demand at that lowest point (those pre-dawn hours) is higher now than it was a decade ago.

Could this be down to an increase in tablets, laptops and smartphones sucking in electricity? An average of 70,000 O2 mobile customers sent texts or made calls nightly between midnight and 5am in the past month, according to an O2 spokesman, with a week-day average of 50,000 rising at weekends. So roughly 233 people were talking to or texting someone every minute at a time when most of the rest of us are asleep.

Vodafone doesn’t give customer figures for its users, a spokeswoman said. But they will explain a pattern of use, which has a rhythm all of its own. Voice and text activity are much more common in daytime and evenings. Vodafone’s 2.2 million Irish mobile users start texting and voice activity in earnest around lunchtime and this peaks at 9pm. Data use, or going online on phones, begins to increase later at around 5pm with its peak also at around 9pm. But when we go online on our phones, we seem to stay there. By midnight, roughly 70 per cent of those peak-time users are still online. This tails off until 5am. But even between four and 5am, significant numbers of Vodafone customers are online. It’s roughly 15 per cent of the number of people who would have been online at the 9pm peak, according to the company.

Are the sleepless of Skiberreen and Seapoint reading 3am tweets or scrolling through Facebook in those early hours? We don’t know. Neither Twitter nor Facebook will give any information about their Irish users’ nighttime activity, raising the question of why social networks, built on the idea of users oversharing, are coy to the point of secrecy about the facts and figures behind that use.

What we do know is that the health benefits of sleep are many. Lose weight, learn more easily and feel happier – if it was a drug, you’d question the claims, but better sleep can help you do all three. So how do you get the best night’s sleep possible?

Dr Lorcan Walsh of Netwell in Dundalk, Co Louth, gave a sleep workshop recently to help people maintain healthy sleep as they age. In a study of older adults, 67 per cent of people reported poor sleep. Sleep apnoea is "quite a large and undiagnosed problem", Walsh says. A sufferer can be waking 30 to 100 times an hour as their airways become obstructed. But it can be diagnosed and treated.

There are plenty of electronic sleep aids, and an online British sleep programme called Sleepio claims to help people eliminate negative thoughts, implement a good sleep schedule and make lifestyle changes to help them sleep better over a six-week course for €60.

Then there’s Ardrahan Lullaby milk, which is milked from cows early in the morning, with “naturally higher levels of melatonin”, produced by the Burns family in Kanturk, Co Cork.

Andrew Coogan advises avoiding an anxiety loop, where you lie awake worrying about the fact that you’re lying awake. Sleep is important and once you engage with the problem, there are plenty of drug-free solutions. And if you’re reading this at 4am, you are definitely not alone.

HOW TO SLEEP BETTER
Make night different to day, with plenty of fresh air and daylight when awake, darkness during sleep
Avoid coffee for four to six hours before sleep and alcohol three hours before bedtime
Sleep in a cool dark room with no screens, phones or tablets. The bedroom should be reserved for sleep and other non-virtual nighttime activity
Avoid work or discussion of emotional ideas before bed. If you have niggling problems, try writing them down and putting them aside before sleep
Go to sleep when you're truly tired
Don't lie in bed awake. Get up, read a book and then go back to bed when you're sleepy
If you wake in the night don't look at the clock – turn the face away
Go to bed and wake up at the same time every day, even at weekends
If you have to nap – keep it short and before 5pm
Eat a light evening meal
Drink enough fluid at night so as not to wake up thirsty – but not so much that you have to pee
Exercise but do it at least three hours before bed

MAKING PEACE WITH SLEEPLESSNESS
Lifelong insomniac Cian Traynor on his strategies for dealing with lack of sleep

Patience has a way of crumbling quickly under the weight of sleepless nights. Petty grievances you wouldn’t normally notice begin to bristle. The toe-curling laugh rattling through the train carriage; the scatterbrained figure holding up airport security, oblivious to the queue behind them. When simple tasks seem arduous and communication skills a luxury you can’t afford, it can feel like you’ve been left behind to navigate on autopilot.

As someone with chronic primary insomnia – long-term sleeplessness without an apparent medical, psychiatric or environmental cause – I know how trying those moments can be. When I was a toddler, my mother would spend hours walking me up and down, trying to wear me out, before slipping me a sedative. Rest is still hard to come by. The longest I’ve ever slept, under medication, is five hours.

My eyes flicker open, my body needs to shift position. I just have to trust that these snatches of sleep add up to something restorative.

In 2009, I spent a night at a sleep clinic. The analysis clocked me waking up 108 times: an average of once every three minutes and 51 seconds. My neurochemistry, I was told, is calibrated so that my brain triggers a steady stream of adrenaline night and day.

Having tried countless solutions without success, I concluded that coming to peace with sleeplessness was the best way forward. Still, the older you get, the harder it becomes to recharge. So, in May 2010, I decided to try another avenue. I was taught how to meditate twice a day for 20 minutes. It settles the mind and nervous system so that you’re resting many times deeper than sleep, clearing away fatigue and dissolving knots of stress.

Feeling less tired has led to a liberating level of composure, making former sources of anxiety seem laughably unnecessary. It has produced a more grounded perspective that disarms the effects of insomnia.

Daily exercise, drinking calming tea and never looking at the clock while in bed help . But the key to shielding yourself from panic as light begins to trickle through the window is knowing you can handle the consequences.

Failing that, sleep will inevitably return elsewhere, claiming you on the couch or at the cinema. You never quite catch up, but by learning to approach life calmly and embracing its fickle rhythms, the big issues are rendered manageable and the small stuff starts to recede.