Understanding Sleep and Why It Matters

Have you ever wondered what happens after you close your eyes at night? Sleep may look like a period when the body simply switches off, but that is not true. Sleep is an active biological process during which the brain and body perform many essential tasks.
While we sleep, our awareness of the outside world decreases, our muscles relax, and our breathing and heart rate change. However, the brain remains busy. It processes information, regulates emotions and prepares us for the next day. The body also restores energy, supports tissue repair and coordinates immune and hormonal functions. Sleep is therefore not wasted time. It is a basic biological need, just like food and water.
Sleep has two main types: non-rapid eye movement sleep, known as non-REM sleep, and rapid eye movement sleep, known as REM sleep.
Non-REM sleep contains three stages. Stage N1 is very light sleep. This is the short transition between being awake and falling asleep. During stage N2, breathing and heart rate slow, body temperature falls, and awareness of the surroundings decreases. Stage N3 is deep sleep, also called slow-wave sleep. During this stage, it becomes harder to wake someone. Deep sleep is closely connected with physical restoration and recovery.
REM sleep is quite different. The eyes move rapidly beneath the eyelids, brain activity increases, and most vivid dreams occur. The muscles of the arms and legs become temporarily inactive, which normally prevents us from acting out our dreams. REM sleep is thought to contribute to emotional processing, learning and some forms of memory.
These stages do not occur only once. We move repeatedly through non-REM and REM sleep in cycles. A cycle commonly lasts about 90 minutes, although its length varies. Most adults experience four to six cycles during a typical night. Deep sleep is generally more prominent during the early part of the night. REM periods become longer closer to morning. This is why cutting sleep short may remove an important part of the normal sleep pattern.
Sleep also supports how we function during the day. It helps the brain organise newly learned information and may strengthen certain memories. Adequate sleep supports attention, decision-making and emotional control. It also helps regulate immune activity and supports physical recovery. After poor sleep, we may feel irritable, forgetful, slow or unusually hungry. One bad night is usually manageable, but repeated sleep loss can interfere with health, performance and safety.
Sleep patterns change throughout life. Newborn babies sleep for much of the day and night. Children need plenty of sleep for development and learning. Teenagers naturally tend to fall asleep early and wake later, although school schedules may work against this pattern. Most adults require around seven to nine hours, but individual needs vary. Older adults may sleep more lightly, wake more often and experience less deep sleep. However, ageing does not mean that restorative sleep stops mattering.
The key message is simple: healthy sleep is not only about spending enough hours in bed. It also involves regular timing, good quality and an appropriate balance of sleep stages. Sleep is not an empty space between two days. It is one of the processes that makes a healthy next day possible.
References

1. Fjell, A. M., & Walhovd, K. B. (2025). Sleep patterns and human brain health. The Neuroscientist, 31(5). https://doi.org/10.1177/10738584241309850
2. Garbarino, S., Lanteri, P., Bragazzi, N. L., Magnavita, N., & Scoditti, E. (2021). Role of sleep deprivation in immune-related disease risk and outcomes. Communications Biology, 4, Article 1304. https://doi.org/10.1038/s42003-021-02825-4