Sleep is a basic need, as essential for mental and physical health as are nutrition and exercise. It allows your body to repair and restore itself so you can function efficiently and energetically during the waking hours.
On average, you spend one-third of your life asleep, although this varies through the years, and less is needed in later life. A one-year old baby will for about 14 hours out of 24 hours, but most adults need just 7 or 8 hours a night. Some say they manage as few as 4 hours; other need 11 or 12 to be at their best.
The occasional sleepless night will do no harm, although it may make you feel awful the next day. Continuous sleep deprivation, however, may affect the way you work, your moods and your physical wellbeing because without sleep the body is unable to repair itself. Going without sleep for as little as three days can lead to confusion, serious mental problems and even hallucinations.
Through research on volunteers in sleep laboratories, scientists now know what happens to the body while you sleep, A normal sleep pattern consists of two parts; REM (rapid eye movement sleep), when your brain is most active (and you dream) and NREM (non-rapid eye movement sleep (when you don't dream).
Volunteers, linked to an electroencephalogram (EEG) that measures brain waves, are woken when electrical activity indicates REM and confirm that they were dreaming. People tend not to remember a dream unless they wake up during it or straight after.
During sleep your brain remains active, analyzing the past day’s events and storing and processing information. Sleep may also be a time of mental healing, because dreaming is though to help you come to terms with any emotional problems.
How Does Sleep Happen?
Once you are comfortable in bed, your eyes start to close and you begin to doze; your body twitches as nerves and muscles relax. During this phase, called shallow sleep, you can be awakened easily by the slightest disturbance because you are still aware of your surroundings. After half an hour or so, sleep becomes deeper; you relax, your heart beats more slowly and you become oblivious to your surroundings. Truly deep sleep follows, during which you are completely relaxed. You remain in one position, your heart rate slows down and your breathing is slow and regular.
It once though that deep sleep continues until you wake up, but scientists have discovered that each of the three stages lasts about half an hour, and that the 90-minute sleep cycle repeats itself through the night. On average, four cycles are needed for a good night’s sleep (meaning you have about 4 separate dreams a night). Toward morning, sleep is more shallow as brain waves speed up again, the heart rate increases, breathing is more rapid and you become more restless. You can seem about to wake up and may even open your eyes, but in fact you are asleep.
Your Biological Clock
The natural sleep pattern is regulated by your biological clock, synchronized by the 24-hour, or circadian, cycle of light and dark. It oversees all body functions, from digestion and waste disposal to sleeping and cell repair.
One of the clock’s influences is the so-called third eye, the pineal gland at the front of the brain. As daylight fades, the gland secretes the hormone melatonin into the bloodstream, which makes you sleepy. Melatonin works with another hormone, cortisol. The cortisol level falls gradually and is at its lowest point after you’ve been asleep for several hours, when your body temperature is also low. At this stage the hypothalamus in the brain prompts the pituitary to direct the other endocrine glands into action to stimulate your metabolism. Your body temperature rises along with the cortisol level and eventually this wakes you up.