Insomnia is the inability to initiate or maintain sleep, or experiencing poor sleep quality. It is reported in about a third of the population in the US. Its consequences may be serious, impairing daytime functioning. Types of insomnia have been defined based upon the duration and pattern of sleep disruption.
Middle-of-the-night (MOTN) insomnia occurs in 20% to 50% of people, though they may not classify it as a formal sleep disorder. It is short-term when it lasts for less than three months, but beyond this, it becomes chronic.
It is characterized by difficulty in maintaining sleep in one block, resulting in a night-time awakening after several hours of sleep, followed by a significant period of persistent wakefulness before the individual can resume sleep. It is therefore also called difficulty in returning to sleep insomnia.