Why waking up from a super long nap makes you feel so wretched.

In theory, waking up from a nap should be a wonderful, restorative sensation.

But anyone who’s punched a few too many zzzs on a lazy weekend afternoon knows overdoing it only makes you feel worse.

This is precisely what happened to me last Saturday when I took a nap at four pm without setting an alarm first. I’d had three coffees by this point, so I figured the caffeine wouldn’t let me rest for long.

Ha! Wrong. Three hours later I woke with a start, dazed and confused with the beginnings of a headache. Where am I? What time is it? It’s dark! Did I sleep through the night? Oh shit, did I sleep for a WEEK?

We’ve all been there.

It’s universally agreed that naps are great, but getting it right is a delicate balancing act.

Why long naps feel so terrible

If it’s any consolation, that wretched feeling you get after extended naps is a common and well-documented phenomenon that even has a name.

It’s called sleep inertia, and the result of abruptly awaking from a deep or slow wave sleep (SWS) — something you’re more likely to experience when you nap for periods longer than 30 minutes. As you can guess, the transition from deep sleep to being awake can be tough.

“You might experience feelings of disorientation, grogginess and tiredness, and your cognitive abilities are actually impaired during this time. This can be an issue, particularly for people who are napping at work or who have to drive or make important decisions soon after awakening,” explains Stephanie Centofanti, Research Associate from the University of South Australia’s Centre for Sleep Research.

Watch: Segmented sleep, explained. (Post continues after video.)

The severity of your sleep inertia can be affected by how sleep deprived you were and the timing of your nap, as well as individual factors.

“Some people actually avoid napping altogether, as they find that they get severe sleep inertia after naps,” Centofanti adds.

The ‘gold standard’ nap

Suffice to say, napping for three hours won’t make you feel good (although I’m sure I’ll do it again sometime). While there’s no “gold standard” for napping, keeping it brief is generally recommended.

“Don’t sleep longer than 15 to 20 minutes, because otherwise you’ll go into a deep sleep. It may also interfere with your ability to fall asleep that night,” explains Dorothy Bruck, Sleep Psychologist with the Sleep Health Foundation.

“On the other hand, if somebody’s very sleep deprived and they really feel that they need a solid nap, then an hour and a half is a good time because that’s about one sleep cycle,” Professor Bruck says. But be warned: you might struggle to fall asleep that night.

Interestingly, there are a number of factors that determine how beneficial and restorative your nap is going to be. Centofanti says although a 10 minute nap in the afternoon has been shown to help recover cognitive performance, a recent Centre for Sleep Research study found a different result at night.

Waking up [from a nap] is hard to do. (Image: Walt Disney Animated Studios)

"[We] found a 10 minute nap taken in the middle of the night, to replicate what a shift worker might do, had no recovery benefits and actually made some people’s mood poorer," she explains.

Individual factors also come into play, so it's impossible to say there's one kind of nap that will benefit everyone.

"For example, a person who is extremely sleep deprived might gain benefits from a 10 to 20 minute nap, but a person who slept properly the night before may not feel better after a nap of the same length," Centofanti says.

"Shorter naps are recommended, but even then the recovery benefit of the nap and severity of sleep inertia can differ from person to person."

Ultimately, we should be trying to work out the nap length that makes us feel more alert — then again, as Centofanti points out, our perceptions or how alert we're feeling don't necessarily align to how well we're performing. (Post continues after gallery.)

Mastering the art of the 20 minute nap.

Napping for 20 minutes neat seems impossible to me, and not for lack of trying. In the past I've set my alarm for 30 minutes (allowing 10 minutes to fall asleep), and by the time it goes off I'm usually still lying awake, willing myself to sleep, damnit.

Professor Bruck says not being able to fall asleep quickly is a sign that perhaps a nap isn't really necessary. "Most people have a nap because they feel like they're able to go to sleep, so if you're lying down and unable to maybe you're just tired and not sleepy," she explains.

Believe it or not, there's a pretty significant difference between the two — tired being a general fatigue of the mind and body, and sleep being the ability or desire to fall asleep.

"If you're tired, you might just want to lie down and have some quiet time for half an hour, but if you're sleepy then you might want to have a nap. If you didn't fall asleep rapidly then maybe you're not sleep; maybe there's a lot going on and you just need a bit of a rest," Professor Bruck says.

Watch: Sleep-deprived mums share their funniest fails. (Post continues after video.)

General napping notes.

In general, napping is a good way to combat the negative impacts of sleep loss, particularly if you're someone who is often deprived of rest (eg. new parents, shift workers). But there are a few things to keep in mind.

"Sleep loss can lead to so many cognitive, mood and physical health issues that people are not often aware of, so if you can nap, then I would not advise against it," Centofanti explains.

"Having said that, sleep at nighttime is always better quality, as our circadian rhythms are primed to help us sleep at night and stay awake during the day. So I would recommend people trying to have a regular sleep routine and getting a full night’s sleep."

It's also not a great idea to take naps in the evening, because this can reduce your 'sleep pressure' and make it harder to fall asleep at night.

Make sure you're getting enough sleep at night, unlike Leslie Knope. (Image: NBC)

Professor Bruck highlights that our bodies enjoy routine, and napping frequently could cause it to start expecting that as the norm. Risky business.

"You can used naps judiciously — sometimes for a catch up sleep it can be a bit delicious and indulgent to have a nice nap," she says.

"But if you do it a couple of days in a row your body will think, 'OK, this is the time I have a nap', and if it's not convenient then you need to think what's the down side of that if you don't nap that day, in terms of how you feel."

How often do you nap? Have you mastered the 20 minute kip?

Featured image: iStock.