THE DEFINITIONS OF SLEEP DISORDERS.
"Insomnia," as reflected by the results of the Stanford poll, is a term broadly used to mean any form of sleep disorder. Specifically, however, it refers simply to the inability to sleep; its Latin roots mean "without sleep." Thus insomnia is just one form of sleep disorder. Sleep disorders can range from difficulty falling asleep to difficulty staying awake during the day. Those who analyze and treat sleep disorders break the subject down into subcategories, each with its own distinctive pattern of causes, symptoms, and consequences. Briefly, these categories of sleep disorders are:
- Disorders of initiating and maintaining sleep (sometimes abbreviated DIMS): DIMS is actually the technical term for what most people mean when they speak of insomnia. This term includes problems with falling asleep and problems staying asleep once sleep has been achieved. For example, you might lie in bed for an hour or more, unable to drop off, or you might snore so loudly as to awaken yourself.
- Disorders of excessive somnolence (DOES; also called hypersomnia): These disorders cause people to feel sleepy during the day or to feel unrested and less able to function. Included in this group are such illnesses as narcolepsy and sleep apnea, which result in insufficient sleep.
- Disorders of the sleep-wake schedule (DSWS): These problems stem from a variety of obvious causes, including jet lag and odd work shifts, or they may be the result of serious internal disruptions in an individual's biological clock (also called "circadian rhythms").
- Parasomnias: These are problems not with sleep itself but associated with, and disruptive of, sleep. Examples include sleepwalking, bed-wetting, and nightmares.
How frequently does each of these types of sleep disorder occur? According to the American Psychiatric Association, hypersomnia, or daytime sleepiness, is actually, and perhaps surprisingly, more prevalent than insomnia, the nighttime inability to sleep. Disorders of excessive sleepiness are found in roughly 50 percent of patients seeking help. Disorders of initiating and maintaining sleep account for approximately 30 percent, while parasomnias occur in 18 percent. Disorders of the sleep-wake schedule are a distinct minority at 2 percent, but that figure may change as scientists learn more about the hidden world of circadian rhythms.