People who are 'perfectly happy' get precisely seven hours and six minutes of shut eye, a new survey reveals.
We already knew that there's a strong link between the amount of sleep we get and our well-being – now it appears there is a very tight margin.
Participants who rated themselves 'mostly happy' people sleep a little bit less than the 'perfectly happy' people, getting seven hours.
And those who said they were 'somewhat happy' snoozed for six hours 54 minutes, the study of 2,000 people shows.
'Less than 6 hours 48 minutes hours of sleep meant complete unhappiness in relationships, constant worry, and never a shred of gratitude,' the report states.
Seven hours is the minimum amount of sleep for adults recommended by the NHS – but perhaps hitting the snooze button for an extra six minutes is a good thing.
In line with previous research, the new study found women struggled the most to get a decent night's sleep, and those reporting the fewest hours also said they were the least happy.
But age is a big factors – the survey by mattress company Amerisleep also found that those 25 or younger get a lot of sleep regardless of happiness level.
Single people report sleeping the most, while separated people sleep the least.
Respondents who got the best sleep were more likely to meditate or take a shower before bedtime.
Activities associated with less sleep include working or playing video games, according to the report.
One in three of us suffers from poor sleep, with stress, computers and mobile devices, shift work patterns taking work home often blamed.
And the price of sleepless nights is more than just fatigue. As well as depression, lack of regular sleep is linked to raised risk of obesity, heart attack, stroke and diabetes – and it shortens your life expectancy.
Clooney says he wakes up five times a night
Insomnia is often attributed to stress and anxiety but its cause could be genetic, according to recent research.
For the first time, an international team of researchers has found seven risk genes for the sleep disorder.
The breakthrough could lead to new treatments for the condition, which blights the lives of one in ten Britons.
A host of celebrities – including Madonna, George Clooney, Lady Gaga and Kim Cattrall – have all spoken about their difficulties in nodding off at night – and now scientists could help explain why.
The findings also suggested there are different genetic variants for men and women – with the latter being more susceptible.
Sleep specialist Professor Eus Van Someren, of Vrije University, Amsterdam and his colleagues mapped the DNA of more than 113,000 people from Britain and the Netherlands
However, while a lot of research tends to focus on the amount of time we sleep, scientists at Brigham and Women's Hospital have found routine is just as important.
They discovered people who go to bed at the same time every night are far more healthy and successful than their more spontaneous peers.
Using sleep diaries, the team measured sleep and circadian rhythms in 61 undergraduates at Harvard College for 30 days, then compared that data to their academic performance.