Tiredness creeps in when it is least required. But a new study claims that a person can bank sleep - and store it up in advance of a tiring event.
To reach the conclusion, American researchers invited a group of volunteers to adjust their sleep patterns so the effect could be monitored, reports The BBC.
For a week, one half of the group were allowed extra sleep, while the others were told to keep their sleeping patterns the same.
Then, the following week, they were all sleep-deprived.
"After this week of either extended or habitual sleep per night, all the volunteers came to the lab and they were given three hours of sleep, per night, for a week," explained Tracy Rupp from the Walter Reed Army Institute of Research.
They were then given tasks of varying complication, and tests showed that those who had banked the sleep were "more resilient during the sleep restriction".
"They showed less performance deterioration with regards to reaction time and alertness than the group that had been given the habitual prior sleep," said Rupp.
"What we're basically saying is if you fill up your reserves and pay back your sleep debt ahead of time, you're better equipped to deal with the sleep loss challenge," the expert added.