Most people have some nights when they cannot sleep. About one in three Americans has a problem with sleep. Many of these people cannot fall asleep. The name of this problem is insomnia. The word insomnia means "no sleep." Some people say, "I didn't sleep all night." But that's not really true. They may sleep lightly and wake up several times. In the morning, they only remember the times they were awake,so they think they wereawake all night.