Answer: Insomnia is a sleep disorder characterized by difficulty falling asleep (initial insomnia) or staying asleep (middle insomnia) or by early awakening with an inability to go back to sleep (terminal insomnia). A sleep disorder such as insomnia can lead to daytime drowsiness, reduced concentration, and a lack of feeling refreshed or rested upon awakening.You can start falling asleep while doing something like driving. Insomnia can be caused by ordinary stress and anxiety or secondary by depression. 50% of the population experiences it a one time or another. 10% have chronic insomnia.