We have all known the misery of a night tossing and turning in bed, as panic mounts over how we'll cope with the exhaustion the next day.

But help is at hand from an unexpected source: your inner caveman. Through in-depth research into the nighttime habits of our prehistoric ancestors, psychologist and sleep scientist , author of , has helped thousands of insomniacs rediscover the joys of a good night's sleep. And he can transform your sleeping habits in just 21 days.

Modern sleep habits have been undermined by technology, artificial lighting, and indoor temperature control. But our bodies and minds haven't evolved at the same pace as tech so we urgently need to reconnect with our evolutionary origins.

Here, Dr van de Laar shares 12 steps for channelling your inner caveman and developing a transformative, game-changing sleep routine.

1 Don't believe everything you hear about sleep: It's often said that insomnia or sleeping problems lead to physical health problems. Sleep problems can mean sleep apnoea, sleeplessness or narcolepsy but, if you look specifically at insomnia, there's little evidence that sleeplessness causes physical health problems. Untreated insomnia might lead to depression and anxiety disorders but not physical problems.

2 Let go of the eight-hour rule: A lot of people think that eight hours is the magic number of hours' sleep and any less will give you health problems and you'll die sooner. For a bad sleeper, that's not really reassuring and can really hamper your sleep. But a 2021 study of 1.1 million people showed that an average sleep lasts between under six hours and almost seven-and-a-half. Thankfully, more or less is fine too. Experiment to identify your optimum sleep length.

3 Use a sleep diary: Record your perception of how you slept every morning for three weeks to compare how you feel. Smartwatches and apps are not recommended for insomniacs who might focus too much on improving sleep scores.

I'm asked a lot: "How much sleep do I need?" There's such a lot of individual variation that I advise people to look at the second week of their holidays. What time of day do you get really sleepy, and what time do you wake up naturally? That way, you can find out your biological rhythm. You have morning people, evening people and everything in between, so this is about asking: "How much sleep do I need?"

But the timing of sleep is also key. If you're an evening person, sometimes it's very hard to wake up. But you can influence your biological clock.

It's very important for evening people to get enough light in the morning. By "enough light", I mean 10,000 lux, which is compared to being outside on a grey day. But in winter, when it's very dark in the morning, you can use a light lamp of 10,000 lux to get going. It makes no difference if the light comes from nature or a lamp. But getting outside means you are moving, and exercise has a positive effect on sleep.

A walk of 20 to 30 minutes, while exposed to light, would be best. It doesn't really matter what time you get daylight. Also, lower the temperature a little in the evening. In the natural environment, the temperature usually cools down when it gets dark. It prepares the body for sleep and you have to be a little bit colder to sleep well.

Good sleep isn't all about the evening and night, though. It's particularly about what you do during the day.

4 Discover your personal sleep needs: For a lot of people, between six and eight hours is normal. But lots of factors influence how you feel when you wake. In periods when you are stressed or need a lot of energy, you might sleep at night but, in the morning, still feel tired. The tiredness people feel in the day is often not directly associated with sleep.

Look at your day and how you use your energy. Work stress or social stress impact energy levels, and sleep isn't enough to compensate. Consider daytime factors that you might need to change to feel more energised. If you exercise, research shows that you feel less groggy the next morning.

Eating carbs in the morning, rather than a protein-rich breakfast, might also help you feel more energised in the morning. Routine is very important, too. Some people shift their rhythm all the time and that can make you more sleepy in the morning.

5 Examine your attitude to lying awake at night: A lot of people think they have to sleep without interruption but lying awake at night for 20% of the time is within the normal range.

In industrialised countries, we have higher sleep pressure because we have a shorter total bed time. If you're in bed for eight hours and sleep for six  hours and 24 minutes, you're still within the normal range.

In traditional tribes, being awake at night was helpful because you could be alert to dangers. Sometimes, lying awake is important. When we are stressed, the body wants more control and to know what is happening. So for people who are stressed or dealing with depression, lying awake is a natural, normal thing. But you can influence this by shortening your total bed time.

6 Shorter total 'bed time'may be better: Insomnia is not about lying awake but how you lie awake. Sleep pressure affects the need for sleep. It's like sleep hunger. Sleep pressure builds, you feel more sleepy, you fall asleep more quickly and tend to sleep with fewer interruptions.

Sleepiness is different to tiredness, which is a lack of energy. Shortening total bed time gives the body more time to build up sleep pressure.

People with insomnia are often in bed for a long time which can decrease sleep pressure and it makes them more awake during the night. So it's about creating a situation where people sleep more quickly instead of lying there trying to sleep.

7 Focus on the reason for lying awake rather than not sleeping: Many people ask: "Why am I not sleeping?" But ask: "Why am I awake?" If you're awake and you're not tense, it might not be a problem.

If you're tense then ask yourself what the underlying problem is and what you might need to change in your life. Trying to control your sleep creates tension and sleep gets further away so try to relax and look at the thoughts that come up.

8 Reduce stress: Mindfulness allows you to observe your thoughts with a little distance and that might be very helpful.

If you're stressed and don't have the capacity for mindfulness, get out of bed and do something relaxing before going back to bed, even if it's not long before your alarm goes off.

9 Keep regular bedtimes: Our biological clock - or circadian clock - likes structure. If you change your rhythm every day, it might make you more sleepy in the morning, especially if you have to get up early.

If evening people have to get up at 6am and then at the weekend they lie in bed until 11am, they might have more problems during the week. So in the morning, don't shift your rhythm by more than 60 to 90  minutes before you get up.

Going to bed at the same time is also best but our bodies have more problems with mornings than evenings. We are more adapted to going to bed later than to getting up earlier. The beginning of the day is most important for your rhythm.

10 Follow the rules of nature: Reconnect with nature, seeking out natural light during the day and using less artificial light in the evening. Exercise and walk, preferably in nature. Even thinking about nature can help you to relax.

11 Respect your circadian rhythm: Once you have a better understanding of your natural circadian rhythm, follow it as closely as possible. Skip the 6am exercise class if it doesn't fit with your rhythm.

12 Don't tempt night-time ghosts: Sleepwalking is treated easily by looking at lifestyle. Many sleepwalkers don't give themselves enough time to sleep, and sleep deprivation leads to more sleepwalking. A rhythm is very important, as are reducing stress and avoiding alcohol or stimulants.

Night-time stimuli can also lead to a tendency to sleepwalk, such as your partner pulling the duvet off or seeing lights pass by if you don't have blackout curtains.

Alcohol is not good for anyone's sleep but problems usually occur when you drink more than two units during the evening.

by Merijn van de Laar is out on January 16 (William Collins, £20)