Related Blogs

Talking in Sleep Explained

Talking in Sleep Explained

Do you or the people around you talk in their sleep? Do you wonder why do people talk in their sleep? Many people are habitual of talking while they are...

Top 8 Reasons You Cannot Sleep

Top 8 Reasons You Cannot Sleep

As important as sleep is, even the best of us miss out on it. Be it stress or illness, travel, or some obligation, the interruptions to sleep are plenty. Lack...


Why Do We Sleep?

Last Updated on February 5, 2021 by Ashwini G

One of the most mysterious aspects of our life is sleep. It is something that none of us can go without, and we don’t even get to know what happens for those few hours that we are unconscious. Besides humans, every other living creature also requires a few hours of rest every day. From animals to birds to plants, every living creature has a certain period of inactivity in 24 hours when they rest. Without rest, no living creature can function normally.

Humans are among those creatures that remain awake during the day and sleep during the night. They are called diurnal creatures. On the other hand, creatures like owls and bats are nocturnal creatures that remain awake during the night and sleep during the day. Regardless of the time of sleep, this is a phenomenon that takes place every single day. You can go without food for a few days, but going without sleep for just one day can make you excessively tired, sleepy, and disoriented. This goes on to show how important this nightly phenomenon is for us.

Evolution Of Sleep

For the ancient man, sleep wasn’t just a period of rest. After the sun went down, a man had nothing else to do because there is no light and also the fear of wild animals. Once it was dark, they retreated into caves to remain safe from wild animals that came out during the night. Because there was nothing else to do during this period, they chose to sleep.

The early Egyptians were said to worship sleep because it was akin to death. Whenever they felt sleepy, they were determined to heed to it because they did not know why they felt that way and what happened during sleep. It was something mysterious that they were afraid of. Even if they did not feel the need to rest, they decided to sleep anyway because they were afraid of the phenomenon.

Before the Industrial Revolution, there was no electricity, and the oil and gas lamps were expensive for the common man. Therefore, people chose to go to bed after sundown in order to conserve oil and gas. People usually went to bed at around 6 or 7 in the evening but woke up after seven or eight hours. During this period, they read, visited neighbors, did the laundry, or had sex. After three or four hours, they went to sleep again, which lasted until morning. Another reason why people back then went to bed so early is that there was nothing else to do. After the Industrial Revolution, when electricity was invented, people started to stay up later because they could work till evening as well as enjoy reading and other forms of entertainment.

There is a lot for humans to do even after the sun goes down. But sleep serves as a period of rest and recharge and helps in re-energizing the cells for the next day. Since there is no wild animal to hide from or conserve oil, sleep is now primarily a period of rest and rejuvenation.

Light Sleep Vs. Deep Sleep

Something that all middle-aged and older adults crave more of is deep sleep. Children are the easiest to drift into a deep sleep; that’s where the term “sleep like a baby” comes from. Babies not only sleep for more than 12 hours a day but also have the deepest sleep. They are not quickly woken up from sleep and also fall asleep very quickly.

Deep sleep is the most rejuvenating. But as a person grows older, deep sleep is not as easy anymore. Most adults complain of insufficient sleep or feeling unrefreshed after waking up in the morning. This is all because of the lack of deep sleep. This can be attributed to hectic lifestyle stress and other factors detrimental to deep sleep. When a person enjoys deep sleep at night, he wakes up feeling more refreshed than usual and also has more energy throughout the day. The elderly usually get the least amount of deep sleep.

Reasons For Sleep

Rest as the reason for sleep is pretty vague. There must be more important reasons behind the mechanism of sleep. This nightly phenomenon is one of the most mysterious aspects of our lives. Sleep is even harder to demystify because when you wake up, we cannot tell what happened inside our brains and bodies while we were asleep. It needs excessive research and scientific studies to find out exactly what happens in the brain and the body when a person sleeps.

However, scientists are yet to pinpoint one single reason behind sleep. Sleep has many functions, and the reason behind why we need sleep are also many.

All the possible reasons for needing sleep that scientists have floated are mere hypotheses. Some of them are:

  • The brain is able to reset itself without getting constant inputs as it does when it’s awake. When the brain is active, it’s not able to perform its healing and reordering functions.
  • When we sleep, the brain processes new information that is gathered throughout the day and also consolidates memories.
  • During sleep, the metabolic rate goes down, which helps in energy conservation. The cardiovascular system also rests during sleep. It has been found that people with high blood pressure experienced a reduction of 20 to 30 percent while they were asleep.
  • During sleep growth, hormones are released, which helps in chemical balancing in the brain and also in repairing dead or aging tissues and cells.

Functions Of Sleep

We tend to think that sleep is a period of inactivity. However, the brain and the body are active when a person sleeps because they are engaged in healing and rejuvenation.

Scientists believe that there are multiple reasons for sleep. When a person sleeps, the following functions are performed:

  • Rest and recovery for the body
  • Protection from predators and other dangers
  • Energy conservation
  • Memory consolidation

The energy that we use in order to function to add the day is stored in cells. These cells burn out while providing the body with energy to function. When we sleep, these cells are healed and repaired, and energy is conserved for the next day. This is how sleep replenishes the body’s energy reserves.

There are certain proteins in the brain that affect cognitive functioning and memory formation in a negative way. These proteins are chemical waste that the brain wants out of the system when a person sleeps. This is called cranial maintenance. When sleep is insufficient, these proteins remain in the brain and later cause cognitive disorders such as Alzheimer’s disease. Without sleep, the brain also finds it hard to process the information that it got throughout the day.

Cycles Of Sleep

Although sleep seems like one long stretch of inactivity, it actually involves a number of stages and cycles. Sleep has four stages, classified as non-REM and REM. The first three stages are non-REM, while the final stage is REM. One sleep cycle is made up of these four stages. In an 8-hour sleep duration, we go through 4 or 5 sleep cycles, each being around 90 minutes long.

The first three stages of sleep are vastly different from the REM phase. The brain is inactive during the non-REM stages, but active during the REM stage; while the brain dreams during the REM stage, the body is paralyzed. During the non-REM phases, growth hormones are released, and the cells are repaired, body temperature is regulated, and memories consolidated. During the REM stages, people have dreams and nightmares.

Without completing all four cycles of sleep, we remain unrefreshed even after 8 hours of sleep. In animals, the period of rest depends upon the energy reserves. Smaller animals use up their energy reserves more quickly and need more sleep. Bigger animals can get by with less sleep because their energy reserves are also greater.

The Reason Behind Sleepiness

There are various reasons as to why we feel sleepy. When our energy reserves start to get depleted, we feel tired and sleepy. When we haven’t eaten in a long time, we feel sleepy. When we are stressed, we feel sleepy.

There are tests to differentiate between normal sleepiness and sleep disorders. Four of the most common tests are:

  • Multiple Sleep Latency Test
  • Maintenance of Wakefulness Test
  • Digital Symbol Substitution
  • Wilkinson Addition Test

When a person or animal is said to be asleep, there are still parts of the brain that are awake and using energy. That’s why it’s not clear why people feel refreshed after a good sleep, because sleep also consumes energy.

Normal sleepiness goes away once the person gets enough rest. But when sleepiness happens when it’s not supposed to happen, it indicates an underlying disorder. Excessive sleepiness is not just an indicator of sleep disorders; it can also indicate other physical ailments, such as anemia, cardiovascular disease, and thyroid disorders. Remember, sleepiness that doesn’t go away after sufficient sleep is a sign of something serious.

Related Blogs

Talking in Sleep Explained

Talking in Sleep Explained

Do you or the people around you talk in their sleep? Do you wonder why do people talk in their sleep? Many people are habitual of talking while they are...

Top 8 Reasons You Cannot Sleep

Top 8 Reasons You Cannot Sleep

As important as sleep is, even the best of us miss out on it. Be it stress or illness, travel, or some obligation, the interruptions to sleep are plenty. Lack...

Contact SleepGuru

Got something to share about the content on this page? Please contact SleepGuru!

8 + 2 =