No mental illness affects more Americans than anxiety. About 40 million American adults—more than 18% of the population—suffer from an anxiety disorder in a given year. Roughly the same number suffer from long-term, chronic sleep disorders, such as insomnia. Insomnia disrupts sleep in many ways. Sufferers have trouble with one or more of the following: falling asleep, difficulty staying asleep, waking up too early, and sleeping but still waking up feeling tired.