Insomnia (from Latin "in" meaning "not", and "Somnus" meaning "sleep") is most often defined by an individual's report of sleeping difficulties. While the term is sometimes used in sleep literature to describe a disorder demonstrated by polysomnographic evidence of disturbed sleep, insomnia is often defined as a positive response to either of two questions: "Do you experience difficulty sleeping?" or "Do you have difficulty falling or staying asleep?"
Thus, insomnia is most often thought of as both a sign and a symptom that can accompany several sleep, medical, and psychiatric disorders, characterized by persistent difficulty falling asleep and/or staying asleep or sleep of poor quality. Insomnia is typically followed by functional impairment while awake. One definition of insomnia is difficulties initiating and/or maintaining sleep, or nonrestorative sleep, associated with impairments of daytime functioning or marked distress for more than 1 month."
Insomnia can be grouped into primary and secondary, or comorbid, insomnia. Primary insomnia is a sleep disorder not attributable to a medical, psychiatric, or environmental cause. A complete diagnosis will differentiate between:
- insomnia as secondary to another condition,
- primary insomnia co-morbid with one or more conditions, or
- free-standing primary insomnia.
Insomnia can be classified as transient, acute, or chronic.
- Transient insomnia lasts for less than a week. It can be caused by another disorder, by changes in the sleep environment, by the timing of sleep, severe depression, or by stress. Its consequences - sleepiness and impaired psychomotor performance - are similar to those of sleep deprivation.
- Acute insomnia is the inability to consistently sleep well for a period of less than a month.
- Chronic insomnia lasts for longer than a month. It can be caused by another disorder, or it can be a primary disorder. Its effects can vary according to its causes. They might include muscular fatigue, hallucinations, and/or mental fatigue. Some people that live with this disorder see things as if they are happening in slow motion, wherein moving objects seem to blend together. Can cause double vision.
- Sleep deprivation
- Thai Ngoc, Vietnamese insomniac, claimed to be awake for 33 years
- Al Herpin, American insomniac, known as the "Man Who Never Slept"