We asked a sleep expert how to have the perfect nap

Going for a nap is a lottery. You either waking feeling revitalised, or as if you’ve gone five rounds with Conor McGregor in a washing machine. Perhaps you prepare for a night out with a 5pm snooze; perhaps you find that Netflix is soporific; but if you do it wrong, you’ll have to throw out the rest of the day (and risk Sunday night insomnia).

We asked leading sleep expert Dr Neil Stanley, former Director of Sleep Research at the University of Sussex, to put the rumours to bed.

Hi Dr Neil, what’s the optimum length of time to nap for?

The ultimate power nap is drinking two cans of Red Bull just before you have your 20 minute nap. The caffeine will take 20 minutes to kick in and you. Red Bull has a controlled dose of caffeine unlike coffee, when you can’t tell how much caffeine is really in it. When you wake up the caffeine in the energy drink kicks in at the same time, so you get a double benefit. For most people this 20 minute so-called power nap will boost your performance by 20% or so.

That’s surprising. When’s the best time to down a Red Bull and kip?

The most obvious time we get sleepy is during the post-lunch dip. This dip has nothing to do with food. It actually happens between two and four in the afternoon. Ideally, this is when you should nap. This natural lull comes from evolution when it was impossible to do anything on the plains of Africa during the afternoon so everyone had to find shade and sleep before starting up again in the evening. That’s when your body expects to have sleep, but we usually push through it.

So napping for anything longer than 20 minutes is bad?

No, not necessarily. There’s two durations of nap: 20 minutes or two hours. You sometimes feel worse after a nap because of sleep inertia associated with deep sleep – the cloudiness or fogginess that can last between 15 mins and two hours. In 20 minutes you shouldn’t go into deep sleep, but in two hours you go through you first cycle of deep sleep and wake up in dreaming sleep we call REM – this is when we’re programmed to wake up naturally. The average person falls asleep between zero and 10 minutes, so you need to factor this time in.

So waking up in deep sleep can actually make you feel worse?

Exactly. You’ll go off with the intension of getting a nap to boost your alertness and energy levels but could potentially knock yourself back by two hours.

I’ve heard some people drink coffee before a nap – are energy drinks better?

Drinking coffee is a rubbish way of taking caffeine as you never really know how much caffeine a cup of coffee contains. It’s a poor drug delivery system. Coffee’s caffeine levels depend on the way it’s mixed and pruned, so it’s never a guaranteed way to get a hit of caffeine. With Red Bull you’re guaranteed a controlled release of caffeine over 20 minutes.

What about when you stay out all night? Would a 20-minute nap have the same restorative effect?

Any sleep you can get will help. The problem is sleep deprivation increases the likelihood of falling asleep deeply and quickly so you end up feeling worse. But if you’re going to have to get through the day after a big night out, then strategic 20-minute naps will help you cope better than just caffeine. It’s a bit like when your mobile phone is really out of charge and you plug it in for five minutes and somehow the battery seems fuller than you’d expect. That’s what a nap does with your body.