© Getty ImagesNapping for the wrong length of time could actually leave you feeling temporarily worse
Sleeping for short periods in the day helps memory and cognitive function. But napping for 30mins or an hour can leave you with a sleep hangover. This is because you wake yourself during periods of deep sleep. Instead nap for 10-20mins for a quick refresh
Or sleep 90mins for a full sleep cycle, with no grogginess when you wake

We have long known that naps have an important function in refreshing and reviving a tired mind.

Some of the greatest thinkers of recent times have been avid nappers - Winston Churchill reportedly relied on regular short naps to help him lead the country through the war.

And yet there remains a cruel stigma against those of us who wish to pop back into bed during daylight hours for a quick shut eye.

But now, in a round-up of scientific research, there is evidence not only proving the real benefits of a kip, but detailed findings that show how varying lengths of snooze have different beneficial effects on the brain.

If you want to wake up from your nap feeling immediately rested then either brief a snooze of 10-20 minutes or a longer 90 minute sleep are your best options.

In a 10-20 minute sleep you will only enter the first, lightest stage of sleep known as non-rapid eye movement, or non-REM sleep. This length of sleep will give you a boost in energy levels and alertness but since your sleep won't be deep, you will be able to wake up easily with little grogginess.

While a 90 minute nap will allow you to fall into a deep sleep, a full hour 30 minutes allows you to complete a complete sleep cycle, giving you plenty of benefits, but also allowing you to rise without that confused sleepy feeling.

Research shows that a snooze of this length will improve procedural memory and creativity.

However don't be fooled into thinking that longer sleeps are automatically better.

Though a nap of an hour or 30 minutes will allow your brain to rest, and so provide benefits, interrupting your sleep cycle at these intervals will likely leave you feeling like you have a 'sleep hangover', known as sleep inertia, and potentially, more tired than before you shut your eyes.

© AlamyA snooze of either 20 or 90 minutes will reap the most benefits and leave you feeling refreshed when you wake up
After being asleep for half an hour, your brain enters a deep level of sleep and waking up will result in sleep inertia of up to 30 minutes before you feel any benefits of having rested.

A 60 minute nap, while allowing for some excellent cognitive rest and benefits, such as improved memory for faces and facts, it is long enough for you to slip into the deepest type of sleep, called slow wave.

Attempting to wake yourself from the middle of slow wave sleep will make you feel pretty fuzzy headed for a while, which may defeat the point if you were trying to feel immediately refreshed in the middle of a hectic schedule.

Sleep expert Dr. Michael Breus explains: 'If you take it longer than 30 minutes, you end up in deep sleep. Have you ever taken a nap and felt worse when you woke up? That's what's happening - you're sleeping too long and you're going into a stage of sleep that's very difficult to get out of.'