Insomnia is characterized by difficulty falling asleep, staying asleep, or both. Sleep is crucial to overall good health. Sleep provides the brain the necessary time to create the normal hormones you need to function efficiently during the day. Mental functioning and physical performance decrease substantially with inadequate sleep and can place you at an increased risk of illness. Poor sleep can result in fatigue, problems with concentration, moodiness, and irritability, and even difficulties with relationships. According to the National Sleep Foundation, most adults should get between seven and nine hours of sleep every night.