Sleep. Are you getting enough? Like sex and money, for more and more people these days the answer to that question seems to be 'no'. Who has time for shut-eye in the 'always on' 21st century?
Snooze and you might miss something great on Twitter. To paraphrase 1980s rocker Jon Bon Jovi, you can sleep all you like when you're dead.
At work, the message comes down from on high. Alpha-male CEOs (even if they are female) vie to outdo one another in the 'How early do you get up?' stakes.
The benchmark answer to that question used to be 6am, with 5.30 reserved for the super-keen, but then outgoing Burberry boss Angela Ahrendts opened a new front in the war against sleep, claiming in a recent interview to be up and doing her emails by 4.30 every morning.
Whether you believe such claims or not, the subtext of these gung-ho public pronouncements is perfectly clear - sleep is for slackers. Times are tough, business is global, job security ever more fragile. If you want to get on - or simply be kept on - you, too, have got to be 'available' round the clock.
That message appears to be getting through. In a recent international study by the US National Sleep Foundation, 18% of Brits reported sleeping fewer than six hours a night during the working week, roughly twice as many people as in most other countries. Only America and Japan were worse off, at 21% and 19% respectively.
No surprises, then, that anxieties about sleep - how much, how often, am I up to scratch? - are now right up there with those traditional sources of all-round angst, our love lives and bank balances, at the top of the list of things that, ahem, keep us awake at night.
'My clinical experience is that sleep deprivation is definitely on the rise,' says Dr Michael Sinclair, consultant clinical psychologist at the City Psychology Group in London. 'In the City especially, there is a lot of fear over job security, leading to overwork, anxiety and worry about sleep.'
So having spent 12 or 14 hours at work, people then come home and lie in bed unable to drop off, fretting about whether they'll still have a job to be stressed out by in the morning. 'It can become a vicious cycle,' he adds.
And even when such obvious pressures are not apparent, sleep remains a low priority. We know we probably ought to get more rest, but there is always a reason not to go to bed, says Sinclair. 'People resent going to sleep because they feel they are missing out and not getting things done. Sleep has become a nuisance, something that gets in the way of us living our lives.'
That's a sentiment with which entrepreneur Clare Johnson, founder of digital executive search business the Up Group, might concur. 'Because of where I am in my life right now, I don't sleep much at all,' she says.
With two kids under the age of three and a fast-growing company to look after, she counts herself lucky to get more than four hours a night. 'I just put sleep to one side. If you are a parent and running your own business, you have to,' she says.
It's a habit that dates back to the early days of the firm. 'When I started the Up Group six years ago, there was just me and my laptop. I was self-funded and had to do everything myself; there was no time for sleep.'
But despite describing what to some would be a living hell, Johnson says she manages fine just the way she is. 'I have the genes for it. I don't worry about sleep, I am happy and fulfilled and I'm not walking around like a zombie. Would I like more? Yes, I would sometimes, but I genuinely don't want eight to 10 hours. I feel worse after too much sleep than I do after not enough.'
Image credit: Richard Allen
Most of us can't function properly on too little kip, however. Studies of army officers show that those who have had only three hours' sleep take 20 minutes longer to come round and get a handle on a fast-moving crisis than those who have had an hour or two more; and a 2011 report from Harvard Medical School found that sleep-deprived workers cost their employers no less than $63m annually in lost productivity.
Part of the reason that we struggle with sleep can be traced to the way our brains work. Put bluntly, our mental circuitry has totally failed to keep up with the pattern and pace of modern life. As far as sleep is concerned, our nervous systems are still stuck in a rose-tinted pastoral idyll where we got up when the sun rose, toiled virtuously all day in the fields and then retired at sunset to sleep the sleep of the just.
Such straw-chewing sensibilities were fine back in the day, but they make us singularly ill equipped to resist the high-tech temptations that now surround us - go to bed or hit iPlayer for the latest Great British Bake Off, with a bit of light Facebooking on the side? It's no contest. So we stay up way past a sensible bedtime, tired but wired and unable to sleep.
'The technology of modern life definitely exacerbates sleep problems,' says Sinclair. There's a culture of doing rather than of simply being; it's too easy not to switch off, even when you do go home.'
Venture capital veteran Jon Moulton of Better Capital, who has a low-tech approach to keeping on top of such potential distractions, agrees. 'Technology can intrude badly into your sleep if you let it - there can be no hiding place from work.
'I have a couple of secretaries to sort through it all for me and I don't give out my mobile phone number,' he adds. 'I sleep seven or eight hours a night and I am pretty determined about it. Sleep is important and you should make sure you get enough. You don't work well without it. People who don't get enough sleep tend to be ratty, irritable and difficult to work with, and the trouble is they often don't realise it themselves.'
How does he cope with the famous 'all-nighters' for which the VC business is renowned?
'When you're doing a deal they all say it will be done by 10pm, but of course it never is. So, these days, I get a few hours' kip earlier in the evening and then join in later, by which point the other poor devils can hardly remember their own names.'
It's also unquestionably the case that the pressure of coping with globalisation has also eaten into what used to be downtime. You've got to be up early in the morning to catch the end of the day in Asia, and then you end up staying awake until the small hours to talk to the US west coast when it comes online. It doesn't leave much time for catching some zeds.
Poor decision-making and a decreased capacity for creative thinking are other consequences of a serious lack of sleep. It can also make you impulsive, according to Professor Jim Horne of the sleep research centre at Loughborough University. 'When you haven't had enough sleep, there is a tendency for you to latch on to random factors and hope for the best. You lose your ability to grasp the bigger picture,' he says.
And, contrary to the image of hard-living, young high achievers who party all night and work all day, the effects are more marked in the young than in the old.
'Young people can enter a state of mild euphoria after being up all night,' Horne believes. 'As you get older, your brain gets more efficient. It works better during waking hours, so you need less sleep.'
There are limits, though. 'No one who has been up all night should be involved in critical decision-making. They can't function properly,' he insists.
Some of our more enlightened big cheeses seem to be getting the point. Huffington Post founder Arianna Huffington recently told a packed conference hall in Johannesburg that sleep is one of the oft-ignored keys to being successful. 'You know all those cliches that sleep is for losers, or I'll sleep when I die? Forget that. Sleep deprivation is for losers. Sleep-deprived people make the wrong decisions. They miss the whispers and the red flags ... Sleep your way to the top!'
So how much sleep is enough? This turns out to be quite a thorny question. The old rule of thumb is that adults need seven or eight hours a night, but this average figure conceals individual requirements varying from as little as four hours to as much as 11.
So it really is perfectly possible for one person to be knackered after six hours' kip while another is bright-eyed after only four or five.
'The eight hours figure is nonsense,' says Horne. 'Sleep is very individual and people know how much they need.'
There is also the question of quality over quantity. 'Five or six hours of good, unbroken sleep is better for you than 10 hours with lots of interruptions,' he adds.
That's because every time you wake, it takes time to get back into deep slow-wave sleep, the kind that leaves you feeling refreshed and raring to go in the morning.
Perhaps the most surprising aspect of sleep, given that even the most red-eyed of us spend a decent chunk of every day doing it, is that nobody is quite sure what it is for. 'It's true we don't know exactly what is going on,' admits Horne, 'because even with modern functional MRI techniques we can't get deep enough inside the sleeping brain.'
Theories range from the evolutionary - that sleep evolved to keep us out of harm's way during the hours of darkness when predators who might fancy a bite are at large - to the thrifty - that sleep is a strategy for saving energy. (These two ideas don't seem to hold water, the first because surely we'd make even easier meat asleep and defenceless, the second because the energy saved by sleeping appears to be minimal.)
But all animals demonstrate sleep-type behaviour, from higher mammals like us down to millimetre-long nematode worms, so something important is clearly going on when we're akip.
The most likely explanation so far is that during sleep, our brains are making sense of the sights and sounds of the day, organising them and filing them away in the light of our existing experiences. 'You have to shut down your consciousness in order to let your brain process the information it has received,' says psychologist Sinclair.
This, he adds, would explain why brain activity when we're sleeping, although cyclical, peaks at or even above what it is when we are awake. There is also evidence that sleep plays an important role in the creation and laying down of our long-term memories.
Whatever goes on after your head hits the pillow, the secret to getting more and better sleep is to try not to worry too much about it, Sinclair counsels. 'Sleep arises naturally as a by-product of being relaxed and calm. It is an outcome; we should try to obsess about it less and just let it be.'
Good advice. And if it doesn't work, you can always console yourself by watching reruns of Breaking Bad on your iPad. Sweet dreams!
How to get a decent night's sleep
- Wind down for at least an hour before bed - read a book or chat to your partner or housemate. Give your body clock a hand by dimming the lights.
- Turn off your phone and iPad and leave them downstairs - if you wake in the night the temptation to check them should be reduced.
- Exercise helps, but in the morning not just before bed. For several hours after exertion, your body temperature remains too high for sleep.
- Caffeine can make you feel less tired, but too much is bad for your cardio-vascular system. Drinking it in the afternoon is a recipe for a bad night.
- Ditto alcohol. A glass of wine may help you relax, but too much and you will wake after a couple of hours and struggle to sleep again.
- Napping during the day can help you to recharge quickly in extremis - just don't go over 20 minutes or you'll feel worse than you did before.