Many people can’t go about their daily lives without their routine afternoon nap. In some countries, like Spain and its siestas, napping is ingrained in the national culture. Many might wonder, however, what are the benefits of napping and whether there are any downsides to it.

If you were looking for straightforward answers to these questions, you won’t find them here. That’s because even though napping is known to recharge people, in some situations mimicking a full night’s sleep, if done improperly this can backfire.

The benefits and downsides of napping

According to the Mayo Clinic, some of the benefits of napping include:

• Relaxation
• Reduced fatigue
• Increased alertness
• Improved mood
• Improved performance, including quicker reaction time and better memory

At the same time, if you oversleep or wake up at the wrong time, you risk:

• Sleep inertia — feeling groggy and disorientated after you wake up.
• Nighttime sleep problems.

Disturbingly enough, one group of researchers from the University of Cambridge, UK linked napping with higher mortality rates. The study suggests that excessive daytime napping might be a useful marker of underlying ill health in an apparently healthy, aging population. This association was most pronounced in people aged 42-65 years. However, the study doesn’t imply that napping is detrimental to your health per se. Rather, the urge to nap can be, in some situations, a symptom of an underlying illness but not a cause.

Dr. Sara Mednick, a psychologist at the University of California, Riverside, and an expert in sleep science echoes this sentiment. In her book Take a Nap! Change Your Life, she writes that if you’re feeling sleepy during most of the day, this is a sign of stress, insomnia, sleep apnea, or some other sleep disorder.

For most people, however, napping is generally a good thing, Mednick says. Her research shows that naps that last anytime between 15 to 90 minutes improve brain functions such as memory and creativity. Napping can also act as a reset button, lowering stress and making you feel energized throughout the day. However, you won’t be able to reap these benefits if you don’t get a good night’s sleep in the first place.

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In her book, Mednick also notes that genetics might explain why some people are natural nappers. These sorts of people, which account for roughly 40 percent of the population, tend to do poorly if they don’t nap. How do you know if you’re a natural napper in the first place? Well, a good hint is if you can regularly nap without falling into a deep sleep.

What the perfect nap looks like

It’s helpful to understand what happens in the brain when we sleep if you want to get really organized about napping and reap the best rewards. These rewards happen to depend on your goals.

When we sleep, the brain goes through several stages or cycles that succeed each other roughly every 90 to 120 minutes. Broadly speaking, these stages can be classed into non-rapid eye movement sleep (NREM) and rapid eye movement sleep (REM). NREM can be further broken down into stages one and two, or light and intermediate sleep respectively, followed by slow-wave sleep. If you wake up in the middle of slow-wave sleep, which is the deepest kind, you’ll get sleep inertia — a groggy feeling that can take hours to shake off. It’s during REM that we dream.

According to Mednick, you can plan your naps diligently to meet your needs. If you’re short on time and need a quick boost, take a 10 to 20 minutes power nap. Sleeping for only this long can be tricky as it can prove difficult to wake up. A good rule of thumb is to nap partially upright.

If you’re tired but need to work, a 60-minute nap will boost your cognitive memory processing. Going through slow-wave sleep helps remember facts, places, and faces but you need to be careful not to wake up in the middle of this stage. It’s different for every person so you might want to go through several trials until you find out how long it takes to get over this stage.

Finally, a 90-minute nap involves a full cycle of sleep, including both NREM and REM. This type of nap aids creativity and emotional and procedural memory, i.e. it helps you consolidate what you just learned, be it how to play the piano or drive a car.

It’s worth noting that if you nap for only 20 minutes and you can dream, it’s a sign that you’re sleep deprived, says Ilene Rosen, an associate professor of clinical medicine at Penn’s Perelman School of Medicine. “10-to-20-minute nap is really the optimal time in terms of bang for your buck,” she added.