Napping has long been a symbol of laziness, but actually it is an essential bodily function that improves our memory, creativity, empathy and problem-solving abilities. Sleep scientists say the gold standard for good physical and mental health is making sure you get between seven and nine hours’ sleep every day, but not necessarily all in one go.“Capitalists in the old days told us that we should do 12 to 16 hours of work for them, and then have eight hours to do what we like, so they wanted us to sleep efficiently in a certain window – that’s where the idea of consolidated sleep comes from,” said Till Roenneberg, a professor of chronobiology at the University of Munich. He has been studying civilisations without electricity, and has observed that people often woke up during the night, took a break and went back to sleep. However, Matthew Walker, a professor of neuroscience at the University of California, Berkeley, and author of Why We Sleep, said people who have trouble falling asleep at night should approach naps with caution, and that everyone should avoid napping after 3pm. “If you nap too late in the day it’s a bit like snacking before main meal, it just takes the edge off your sleep hunger at night,” he said. The ideal length, according to the scientists, is 20 to 25 minutes. Any longer and you’ll fall into a deeper sleep cycle, which lasts for about 90 minutes. This means when you wake up you will experience “sleep inertia”, or grogginess.Colin Espie, a professor of sleep medicine at the University of Oxford, recommends the caffeine nap, which is also advised for sleepy drivers in the Highway Code. This involves drinking coffee before falling asleep, which then jolts you awake once it kicks in 20 minutes later. But he thinks this should be used as an emergency measure only. “If you’re finding naps restorative then you’re probably sleep deprived. You should be making sure you’re getting sufficient sleep at night instead,” he said.