When you sleep, your body rests and restores its energy levels. However, sleep is an active state that affects both your physical and mental well-being. A good night's sleep is often the best way to help you cope with stress, solve problems, or recover from illness.There are two types of sleep: Non-Rapid Eye Movement (NREM) and Rapid Eye Movement (REM). The first four stages of sleep are NREM, and the fifth is REM.
Stage One: This stage of sleep is very light, and usually lasts for about five to ten minutes. Sleepers are very easily awakened, and may experience a feeling of falling that causes hypnic myclonia (that random twitch right before you fall asleep).
Stage Two: This stage of sleep is also light, but deeper than the first. It lasts for about 20 minutes, during which time the brain produces sleep spindles (a burst of oscillatory brain activity). This stage alternates muscle relaxation and muscle tone. Also during Stage Two, body temperature decreases and heart rate slows.
Stages Three and Four: Both are transitional stages between light and deep sleep. Stage four is more intense than stage three, but both are slow-wave (delta) sleep. Stage four usually lasts about 30 minutes, but if a person wakes up during either stage, they will be fairly disoriented.
Stage Five: The body has entered REM sleep. This is where most dreaming occurs because brain activity is increased. During this stage, other body muscle groups are paralyzed, and eye movement, breathing, and heart rate increase. REM sleep is also known as paradoxical sleep.
A typical sleep cycle is: 1, 2, 3, 4, 3, 2, 5. The first complete sleep cycle usually lasts 100 minutes, but will gradually get longer, as the REM stage increases each time the cycle is completed. Deeper sleep occurs more often in children, and people will tend to sleep more lightly as they age. NREM sleep is also very important because it is the time when the body repairs and regenerates tissue, builds bone and muscle, and strengthens the immune system. For these reasons and many more, it is crucial to get enough sleep each night.yr
Information cited from:
http://www.webmd.com/sleep-disorders/excessive-sleepiness-10/sleep-101
http://sleep-geek.com/Articles/Article?articleId=2269
