Typically this altered sleep is associated with some change in one's ability to function during the daytime. However, for many individuals the problem is severe, chronic or of unknown etiologyuand causes the patient to seek medical attention.
Insomnia is the most common symptom encountered in the general population.
Population surveys indicate that between 20 and 33 percent of the population complain of difficulty with sleep. Insomnia is also more common among psychiatric patients, especially those suffering from depression. Low socioeconomic status, poor education, chronic medical illness, recent life stress, and the use of alcohol are also associated with an increased incidence of insomnia. Surveys of the general population have found that between 0.5 and 5 percent of those surveyed complain of sleepiness. Variations in the prevalence depend on the specific population sampled and the questions that are asked.