Sleep disorders are subdivided into the categories Dyssomnias (characterised by abnormality in the amount, quality or timing of sleep) and Parasomnias (characterised by abnormal behaviour or physiological events occurring in association with sleep, sleep stages and the transitions between sleeping and waking).
The Dyssomnias. Five disorders are listed under this heading: Primary Insomnia, Primary Hypersomnia, Narcolepsy, Breathing-Related Sleep Disorder and the Circadian Rhythm Sleep Disorder.
Primary Insomnia. The term insomnia refers to a condition in which it is difficult to fall asleep. The condition is common to many people who are unable to sleep or find it impossible to remain asleep for a period of time sufficiently long to ensure proper rest. One should speak in terms of insomnia only in cases in which the low quantity of sleep causes the sufferer real physical or mental problems, but not when a subject sleeps for a short period of time and in any case feels rested and satisfied with the sleep. Some people in fact do not need much sleep: a few hours are sufficient to provide them with sufficient rest, and this is because people have different physical requirements. Insomnia is a disorder; it is a symptom which reveals the presence of an alteration of the normal functioning of the organism. There are many possible causes that determine the onset of this disturbance and the different types of insomnia.
Transitory insomnia is sleeplessness that arises following an event which causes considerable arousal, an intense emotion or some good news or bad news. In such cases the anxiety that derives from an external factor creates such a degree of arousal within the nervous system that the brain remains alert and in a state of permanent wakefulness. This may occur for example before sitting an examination (see Performance Anxiety) or an important event. Certain physical complaints or disturbances can cause this condition, such as a heavy cold or particular external events such as travelling into a different time zone after a long journey and noises that are far too loud.
Short-Term Insomnia, as the name itself suggests, indicates the form of insomnia which lasts for a limited period of time only, and generally not longer than two or three consecutive weeks. The causes are often of an emotional nature and following important, difficult or tragic life events (see also ‘Post-Traumatic Stress Disorder’). Insomnia occurring as a consequence of mourning and grieving the loss of a significant partner or relation or as a reaction to the sickness of a loved one are examples. The stress determined by these situations influences the mind and body to such a degree that it becomes difficult to sleep properly or it is no longer possible to fall asleep if not after hours of tossing and turning in bed on account of the fact the sufferer is incapable of not thinking about a serious problem that occurred during the previous day. Eventually this kind of insomnia tends to decrease and vanish but in some particularly severe cases it may carry on for a considerable length of time.
Chronic insomnia is a condition which is habitual and persistent. There are many different factors that may determine the disturbance; these include psychological, physiological or environmental problems or dramatic events. Any kind of event can trigger the onset of insomnia, which may resolve in a relatively short and bearable period of time but it may also become chronic and may become an important disorder in consideration of related and consequent problems. On becoming excessive, a daily life habit such as drinking alcohol may result in chronic insomnia, a condition that could also develop as a consequence of being subject to constant stress, which might occur for example in an unsatisfactory occupational situation (see Stress, Personality and Work).
Narcolepsy. A sleep disorder characterised by excessive somnolence during the daytime. The disturbance is experienced despite the fact the subject has slept for a sufficient period of time through the previous night. Unlike hypersomnia, in which the increase of sleep is a gradual process and is not restorative, in Narcolepsy it presents as a sudden attack, at the end of which one feels rested (until the return of another attack of sleep). These episodes may last for a few minutes, about half an hour or occasionally for an hour, and may also occur at unexpected times. Two characteristics of the Narcolepsy Disorder are: