Insomnia is difficulty in falling asleep, staying asleep, and waking up too early in the morning. It is a common health problem that can cause excessive daytime sleepiness and a lack of energy. Long-term insomnia can cause an individual to feel tired, depressed or irritable, have trouble paying attention, learning, and remembering, and not be able to perform fully on the job or at school. Severe insomnia can result in neurochemical (brain chemical) changes that may cause problems such as depression and anxiety, further complicating the insomnia.
Insomnia increases sleep latency, or the length of time that it takes to go from full wakefulness to falling asleep. During the daytime, a sleep latency of 15-25 minutes is considered normal.
Insomnia is classified as transient (occasional), mild, and severe, depending on how often it occurs and for how long. Chronic insomnia is defined as having symptoms at least three nights per week for more than a month. Insomnia that lasts for less than a month is known as short-term, or acute insomnia.
Most adults have experienced insomnia or sleeplessness at one time or another in their lives. An estimated 30-50% of the general population of the United States has been affected at one time or another by acute insomnia, and 10% have chronic (long-term) insomnia.
Insomnia affects all age groups, but its prevalence tends to increase with age. Insomnia affects approximately 40% of women and 30% of men at any given time. The average American gets seven hours of sleep nightly, instead of the eight to ten hours recommended by doctors.

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types of insomnia

Transient insomnia: Transient insomnia lasts from one night to a few weeks. Most people suffer occasionally from transient insomnia due to different factors in their lives, such as jetlag or short-term anxiety. If transient insomnia continues to occur more frequently, but still not nightly, the insomnia is classified as intermittent.
Acute insomnia: Acute insomnia is the inability to consistently sleep without interruption for a period of three weeks to six months. Stress or psychological problems such as anxiety are the most common trigger for short-term or acute insomnia.
Chronic insomnia: Chronic insomnia is long-term, and persists almost nightly for more than one month.
Fatal familial insomnia: Fatal familial insomnia, or FFI, is a very rare inherited disease of the brain. The dominant gene responsible for FFI has been found in just 28 families worldwide. If only one parent has the gene, the offspring have a 50% chance of inheriting it and developing the disease. The disease's progression into complete sleeplessness is untreatable, and ultimately fatal.