Insomnia is the inability to achieve a complete night's sleep over one or more days, weeks, or months. It is not necessarily a decline in the quantity of sleep, but rather the quality of sleep. If you take quite some time to fall asleep or wake up several times during the night, you still may be getting adequate amounts of quality sleep. The characteristics of your sleep cycle determine the quality of your sleep.
There are five basic stages of sleep. These range from a relaxed wakefulness (pre Stage 1 / Stage 1) to deep sleep (Stage 4) to a dream or Rapid Eye Movement (REM) state. A complete cycle takes up to three hours and occurs several times a night. As the night goes on, the periods of REM sleep increase while deep-sleep periods grow shorter. You tend to have a lighter sleep in the second half of the night. This is also the period when most people awaken. Your first half of the night is often spent in "core sleep" -- a period of deep, restful, sleep. Even though you may wake up at dawn, if your core sleep was well spent, you will be alert and ready for the day ahead.
There are three categories of insomnia: transient, intermittent, and chronic. Transient insomnia occurs from one day to a few weeks. Intermittent insomnia is occasional instances of transient insomnia. Chronic insomnia occurs almost every night for one month or more.
Women, especially those over 40, tend to experience insomnia 40% more often than men. Elderly people also have a higher incidence of insomnia. However, this may be caused by illness or drug interactions.
