DON’T believe the hype surrounding power naps, experts say.

Longer sleeps make you feel groggier when you wake up, but they give you many more benefits than a quick 20-minute nap.

“The longer you’re asleep and the deeper asleep you are, the longer it takes for you to get going again, but the recovery value is better,” says sleep researcher Drew Dawson, director of the Appleton Institute at CQUniversity.

Power naps are currently a hot topic. At a time when about one in three people aren’t getting enough sleep, experts are saying more naps might make for more functional workplaces, the Wall Street Journalreports.

It pointed to companies such as Google and The Huffington Post which have installed “sleeping pods” in their offices that cost between $US8995 and $US12,985.

But if you like the idea of a quick power nap and are the type of person who finds it difficult to fall asleep, there’s not much you can do.

“There seem to be a group of people who nap quite easily and find it quite easy to fall asleep,” Prof Dawson said.

“Then there’s a group of people that even if they’re quite tired don’t tend to nap. The biological basis of that is not known.”

How and when to nap

To increase your chances of falling asleep, you should be lying horizontal in a cool, dark, quiet place.

“Most of it is common sense. In crude terms between one and four in the afternoon is quite easy to nap. Between five and eight is almost impossible,” Prof Dawson said.

The length of your nap should depend on why you’re taking it. If you want a “quick boost of alertness”, 10-20 minutes is enough (and is probably all you can get away with at work).

However, if you want to improve your cognitive memory processing you need an hour’s sleep, says Sara Mednick, an assistant psychology professor at the University of California.

And in order to improve “creativity and emotional and procedural memory” a 90-minute nap is required, Dr Mednick told the Journal.

A 2012 study tested this theory by splitting 36 students into three groups and giving them a memory task. After the task, one group took a 60-minute nap, one group took a 10-minute nap, and one group didn’t nap at all.

The groups that napped performed much better when their memories were retested, said study author Sara Alger, from the University of Notre Dame in Indiana, US.

But a week later the 10-minute nap group performed just as poorly as the group that didn’t nap at all. It was only the 60-minute nap group whose memory was extra sharp.

The business of actually falling asleep is far less scientific.

“If you’re tired you’ll fall asleep,” Prof Dawson says. “If you’re not you probably won’t.”