Scientists now generally agree that the sleep cycle is divided into five stages: the onset of sleep, light sleep, deep sleep, and rapid eye movement (REM) sleep. The first four stages are also known as non-rapid eye movement (NREM) sleep, as there is no eye movement during these phases.

A complete sleep cycle lasts approximately 90–100 minutes. If we wake up at intervals that are multiples of 90 minutes—such as after 6 hours or 7½ hours—we will feel more alert.

The actual amount of sleep each person needs varies from individual to individual; some require as little as four hours, whilst others need ten hours. Therefore, the criterion for determining whether one has had sufficient sleep is not the duration of sleep itself.

In fact, as long as you wake up feeling energetic and in good spirits, this indicates that you have had sufficient sleep and that your sleep quality is reasonably good; conversely, it suggests that your sleep has been poor.

According to Wikipedia’s definition, sleep deprivation refers to a lack of sufficient sleep duration and/or quality to support an individual’s alertness, performance and health.

Put simply, it is a lack of sleep that affects a person’s mental and physical health. I wonder if you’ve noticed that if we stay up late the night before, the next day we feel our reactions are slower, we struggle to concentrate and our cognitive abilities decline; this is actually a manifestation of sleep deprivation.

How long can a person actually go without sleep?

In late December 1963, Randy Gardner, a student in the United States, began a sleep deprivation experiment with the help of friends and a professor.

During the first few days of the experiment, Randy was full of energy, and the lack of sleep did not seem to affect him greatly; however, as the experiment progressed, he began to experience extreme irritability and hallucinations.

After 264 hours, the professor brought the experiment to an end; although Randy indicated he could continue, the professor believed that carrying on would put Randy’s life at risk.

Those 264 hours (11 days) thus became the world record for the longest period a person has gone without sleep.

The insomnia we commonly refer to is characterised by the following typical symptoms: difficulty falling asleep (taking more than 30 minutes to fall asleep), waking up too early, waking frequently during the night, vivid dreams, shallow sleep, and feeling dazed and unwell upon waking.

There are many causes of insomnia.

One of these is a reduction in the secretion of melatonin in the body.

Melatonin is a hormone secreted by the pineal gland in the human brain; it plays a role in regulating our body’s circadian rhythm.

The retina transmits information about the intensity of blue light detected in the environment to the pineal gland; when blue light levels are low at night, the pineal gland begins to secrete melatonin, making us feel sleepy. Consequently, if the body secretes too little of this hormone at night, people may experience difficulty falling asleep.

This condition can be alleviated by taking melatonin supplements; however, it is worth noting that melatonin is an endogenous hormone, and long-term excessive intake may directly suppress the body’s natural synthesis and secretion of melatonin, thereby leading to sleep disturbances. It is essential to take it in accordance with the dosage recommended by a qualified doctor.

Furthermore, there are many other causes of insomnia that are not related to melatonin, such as depression, anxiety, physical illnesses, medication and stimulants. In such cases, we need to develop a recovery plan with the help of a qualified doctor.

Here are some methods to help you alleviate insomnia.

① Create a comfortable sleeping environment for yourself. Arrange your pillow and duvet so that you are comfortable, keep the room as quiet as possible, turn off the lights, draw the curtains to keep the room relatively dark, and ensure the room temperature is slightly on the cooler side.

② Take a bath an hour and a half before bedtime; after bathing, your body temperature will rise slightly, and as it cools down, you will begin to feel slightly drowsy.

③ Reduce your screen time before bed. The blue light emitted by electronic devices suppresses the body’s production of melatonin, which can make it harder to fall asleep.

④ Clear your mind; try not to dwell on the events of the day before bed. Sometimes, the more you think about them, the harder it is to fall asleep. You might try listening to some soothing, relaxing music before bed. Here are two active relaxation techniques:

Abdominal Breathing Relaxation Technique: Sit down or lie flat on your bed, relax your body and close your eyes. Place your hands on your abdomen and feel it rise and fall as you breathe; your abdomen should expand as you inhale and contract as you exhale. Inhale slowly for three seconds, then exhale slowly for three seconds, and repeat this for three to five minutes.

Progressive Muscle Relaxation: Lie on your bed and, one by one, tense and then gradually relax the muscles throughout your body. Taking your arms as an example, start by clenching your fists to feel the muscles in your arms tense, then unclench them to experience the sensation of relaxation. Continue practising in this way, working your way from head to toe.

⑤ Increase your physical activity moderately during the day; when your body is tired, you will naturally find it easier to fall asleep. However, remember not to engage in strenuous exercise within two hours of going to bed.

⑥ Try to go to bed and get up at the same time every day to establish a regular sleep routine. This may be difficult at first, so you can simply go to bed only when you feel sleepy and limit your activities in bed, ensuring that the bed is reserved solely for sleeping. Over time, your body will learn that the bed is only for sleeping, making it easier to fall asleep.