Most of us have adopted nightly rituals. Winding down by reading a book, listening to music or some other relaxing activity (OK, Netflix), brushing our teeth, turning off the bedroom lights and assuming our preferred sleeping position, all of which cue our minds to switch off. Dr Walker advocates a hot bath before bed to both relax and trigger a sleep-inducing drop in body temperature.

But sometimes, the association with falling asleep can break down; insomnia sufferers can condition themselves to associate the bed with being more awake. Cognitive behaviour therapy for insomnia resets that with “stimulus control” in which the bed is restricted to sleeping and sex: no reading, working, watching or eating. “If you can’t fall asleep then don’t lie there,” says Dr Gupta. “Get up, do something else relaxing, like reading, and only go back to bed when you feel sleepy.”

To quote Macbeth, sleep is “great nature’s second course/chief nourisher in life’s feast”. Order a second course or otherwise feast before bed, however, and your sleep won’t be so great. Large meals can cause indigestion, writes Dr Walker, which interferes with sleep – as does having to wake up in order to pee.

If increasing REM sleep is a priority then don’t drink alcohol in particular: you might feel like it takes the edge off but booze keeps you in the lighter stages of shuteye and, in heavy quantities, can impair breathing. “You also tend to wake up in the middle of the night when the effects of the alcohol have worn off,” says Dr Walker.

The stimulating effects of caffeine – found in coffee, some teas, chocolate, colas and monstrous energy drinks – can last up to eight hours, so bear that in mind mid-afternoon. And when the waiter asks if you want coffee after dinner, feel free to decline.

Sleep is governed by an internal clock that’s regulated by light and dark. So where you sleep should ideally be dark. (If not, put up thick curtains or blackout blinds, or wear an eye mask.) It should also be cool, which helps you sleep better. And it should be free of gadgets such as phones, which not only distract you but emit light that disrupts said clock. (Dr Walker suggests turning your external clock around so you can’t see the time: calculating how long you’ve been lying awake or how much sleep you’re not going to get certainly won’t help.)

Familiarity is also important, says Dr Gupta, which is why you toss and turn on the first night in a strange place such as a hotel. He advises travelling athletes to take personal effects, such as pictures of loved ones, from their bedrooms at home and, when they arrive, set out the items, unpack their clothes and “own the space”.

Physical activity can improve sleep quality and quickness of onset, although how isn’t clear: maybe because it resets your internal clock, or causes a drop in body temperature (after the initial rise), or helps you figuratively chill out; moderate aerobic exercise in particular can improve deep sleep.

But harder and faster doesn’t necessarily mean sleepier. You might think super-active athletes would sleep like champs, but in fact blocks of high-volume or high-intensity training often coincide with periods of poor sleep, says Dr Gupta, mainly due to the additional physiological stress. Exercise also releases endorphins that can keep you alert for hours afterwards (although the effect is highly individual).

The best exercise for improving sleep might be a walk outside, ideally within an hour of waking: exposure to sunlight, especially in the morning, sets your internal clock right.