If you only got six hours' shut-eye last night, there's no need to lose sleep over it.
Because despite the widely held belief that we need eight hours a night, scientists say six to seven hours is natural.
And they even claim it is a myth that modern living is robbing us of precious time in bed.
The researchers came to their conclusions after examining the sleeping patterns of three present-day tribal societies - whose lives are fairly similar to those of our ancient human ancestors.
The San tribe from Namibia, the Hadza of Tanzania and the Tsimane tribe from Bolivia were chosen because their traditional lifestyles lack the technology and trappings of modern life.
Special watch-sized devices which measure sleeping and waking times as well as light exposure recorded more than 1,000 days' worth of data for 94 adults.
Most of those studied slept for under seven hours a night. The average amount of time spent sleeping was just six hours and 25 minutes. This is much less than the eight hours often recommended in western societies.
Despite this, the people studied were healthy, with lower rates of obesity, better blood pressure and healthier hearts than those in industrialised societies. They were also fitter.
Advising short-sleepers to rest easy, the researchers said: "This has important implications for the idea that we need to take sleeping pills because sleep has been reduced from its natural level by widespread use of electricity, TV, the internet and so on."
Gandhi Yetish, who led the researchers from the University of California, said: "There's this expectation that we should all be sleeping for eight or nine hours a night, and if you took away modern technology, people would be sleeping more. But now, for the first time, we are showing that's not true."
Researcher Jerome Siegel added: "The argument has always been that modern life has reduced our sleep time below the amount our ancestors got, but our data indicates that this is a myth."
The study, published in the journal Current Biology, also cast doubt on the idea that we are going against nature by staying up after dark.
Despite not having electricity, the people studied did not turn in at dusk. Instead they stayed awake for an average of three hours and 20 minutes after sunset.
Professor Siegel said: "The fact that we all stay up after sunset is normal and doesn't appear to be a new development, although electric lights may have further extended our natural waking period."
The tribes did not seem to take many naps or suffer from insomnia, with two of the cultures not even having a word for the disorder.
The findings do, however, provide some insight into how to control our sleeping patterns. With no central heating, temperatures tended to fall throughout the night.
The tribes woke up when the mercury reached its coldest point, even when that was after daybreak. This resulted in them getting up at roughly the same time every day.
Professor Siegel said: "In most modern environments, people are sleeping in a fixed temperature, even if it's reduced from daytime levels. It may well be that falling environmental temperature is integral to sleep control."
- Daily Mail