CRUCIAL SLEEP HYGIENE RULES:

FIX YOUR WAKE-UP TIME

“The most important predictor of improving sleep is when you wake up,” says Lefkowitz.

“If you get into a habit of going to sleep at different times at night, it’s really hard to reset the body’s circadian rhythm. Every day of the week you should be getting up within 20 minutes of the same time.”

Once you’ve worked out what time you can realistically wake up, count backward in 90-minute cycles to work out your bedtime.

If you miss it one night, you’re better off waiting until the start of the next cycle.

EAT FOR SLEEP

“If you eat a high-sugar diet or you eat sugar or drink alcohol before you go to bed, a few hours into sleep your blood sugar drops and your body wakes you up to rescue itself,” says Lefkowitz.

As well as limiting sugar and alcohol, stop eating and drinking any liquids at least two hours before sleep to avoid nighttime trips to the bathroom.

After a meal, body and brain are busy working on digestion which means they aren’t as calm as they should be for sleep.

HAVE SLEEP-PROMOTING BEDROOM SPACE

Make sure your duvet isn’t too warm or too cold to wake you up.

Keep your bedroom cool: just over 18 C is recommended. Avoid blue light. Sources include digital screens and fluorescent and LED lighting.

You don’t have to be in a blackout before bed, however: warm-colour lights, like red or orange bulbs or candlelight, are fine.

Silence is also key.

EMBRACE THE NAP

Even a short snooze improves people’s mood and alertness, concluded a 2009 review.

But how long should you nap? Experts don’t agree. Researchers at the University of Pennsylvania recently ran a study involving 3,000 people. Those who took an hour-long nap after lunch performed better, but if the nap was longer or shorter, they performed significantly worse.

Littlehales suggests a daily 20-30 minute “zone-out” period. It should take place after lunch and it doesn’t matter if you don’t sleep: the disconnection from daily life is enough.