Insomnia is the most common sleep complaint among Americans.
It can be either acute, lasting one to several nights, or chronic, even lasting months to years. When insomnia persists for longer than a month, it is considered chronic. According to the National Center for Sleep Disorders Research at the National Institutes of Health, about 30-40% of adults say they have some symptoms of insomnia within a given year, and about 10-15 percent of adults say they have chronic insomnia. People who have trouble sleeping every night without exception for months or years are fairly rare. More often, people experience chronic-intermittent insomnia, which means difficulty sleeping for a few nights, followed by a few nights of adequate sleep before the problem returns.