Sleep is integral to life. It is present in all sorts of life on earth, from humans to rabbits, sharks to gerbils. Humans generally spend about one-third of our lives asleep. There are two main types of sleep. Sleep begins with the first stage, non rapid-eye movement (NREM) sleep. This stage is characterized by periodic eye movement. This is called light sleeping. Stage 2 is when one is considered to truly be asleep. The sleeper becomes separated from their environment, and the body establishes a regular pattern for the heart and lungs. Stages 3 and 4 are interlinked because they are very similar, with Stage 4 being a more intense version of Stage 3. These stages are considered to be deep sleep, and are the most restorative to the body.
Stage 5 is known as Rapid-Eye Movement (REM) sleep. Referring to REM sleep is a bit of a misnomer though, as REM sleep occurs periodically over the course of sleep. This is considered to the lightest phase of sleep. REM sleep is important as this period is when the brain is almost as active as when it is awake. REM sleep is not completely understood and therefore several theories on its purpose have been proposed. These range from the opportunity for infants to form more lasting neural pathways, to the evolution of the response to predators known as "playing dead," to the most popular, memory consolidation. While scientists continue to study REM sleep, what is beyond dispute is REM sleep’s importance.
It is a myth that humans need eight hours of sleep per day. While the average adult human requires eight hours, most humans need between seven and nine hours of sleep per day. Sleeping only four hours a night will cause the body to experience performance issues. It can even make one more likely to be depressed or abuse substances. Those who only sleep four hours have become inured as to how much the lack of sleep is affecting them.
There is no magic number for the amount of sleep you need. A good rule of thumb is if you have trouble staying awake during the day, or if you are falling asleep through that morning class or afternoon meeting, you are most likely not getting enough sleep. Sleep is important because of what the body does during the time asleep. Contrary to popular belief, the brain does not "turn off." Rather different functions take place. Delta waves, a specific type of brain wave, actually increase during sleep, as does the endocrine system (the glands that secrete various hormones into the blood).
Humans can even develop a sleep debt, where a lack of sleep leads to problems such as sleepiness. As the debt gets worse greater issues such as gaining weight, becoming sick, or becoming less functional become apparent. A lack of sleep is also believed to help develop Type 2 diabetes and even cancer. This debt is hard to remove. Trying to make up your sleep debt will actually make the problem worse. The human body needs consistency in order function at its peak, and by throwing off your body cycle by sleeping in too long, you actually decrease your body’s ability to sleep normally. So try to set a sleep schedule that you can stick to. Your body will thank you for it.