Middle-of-the-night insomnia

Middle-of-the-night insomnia, or "sleep maintenance insomnia", also called terminal insomnia in contrast with "initial insomnia", is characterized by having difficulty returning to sleep after waking up during the night or very early in the morning. Initial or "sleep-onset" insomnia consists of having difficulty falling asleep at the beginning of sleep.

The disrupted sleep patterns caused by middle-of-the-night insomnia make many sufferers of the condition complain of fatigue the following day. Excessive daytime sleepiness is reported nearly two times higher by individuals with nocturnal awakenings than by people who sleep through the night.^[1]

Sleep research conducted in the 1990s showed that such waking up during the night may be a natural sleep pattern, rather than a form of insomnia.^[2] If interrupted sleep (called "biphasic sleeping" or "bimodal sleep") is perceived as normal and not referred to as "insomnia", less distress is caused and a return to sleep usually occurs after about one hour.^[3]