Because the need for sleep varies considerably from person to person, it is difficult to decide what constitutes sleep deprivation. Certain individuals apparently function well on 4 h or even less of sleep per 24-h period, and others, who sleep long hours, claim not to obtain maximum benefit from it.
The term insomnia signifies a chronic inability to sleep despite adequate opportunity to do so; it is used popularly to indicate any impairment in the duration, depth, or restorative properties of sleep. There may be difficulty in falling asleep or remaining asleep, awakening may come too early, or there may be a combination of these complaints. Precision as to what constitutes pathologic insomnia is impossible at the present time because of our uncertainty as to the exact amounts of sleep required, and the role of sleep in the economy of the human body. All that can be said is that some form of sleeplessness is a frequent complaint (20 to 40 percent of the population) and is more prominent in the elderly and in women. Only a small proportion of persons who perceive their sleep to be inadequate seek professional help or use sleeping pills, according to Mellinger and colleagues.
Two general classes of insomnia can be recognized—one in which there appears to be a primary abnormality of the sleep mechanism, and another in which the sleep disturbance is secondary to, or perhaps more accurately comorbid with, a medical or psychologic disorder. Polysomnographic studies have defined yet another subgroup who actually sleep enough, but who perceive their sleep time to be shortened or disrupted (“paradoxical insomnia”).
This term is reserved for the condition in which nocturnal sleep is disturbed for prolonged periods and none of the symptoms of anxiety, depression, pain, or other psychiatric or medical diseases can be invoked to explain the sleep disturbance. In some patients, like those described by Hauri and Olmstead, the disorder is lifelong. Unlike the rare individuals who seem to be satisfied with 4 h or even less of sleep a night, insomniacs suffer the effects of partial sleep deprivation and resort to medications or alcohol. Their lives come to revolve around sleep to such an extent that they have been called “sleep pedants” or “sleep hypochondriacs.” Although statements on the quantity and quality of sleep given by insomniacs are often not to be taken as entirely valid, Rechtschaffen and Monroe have confirmed that most of them do, indeed, sleep for shorter periods, move and awaken more often, spend less time in N3 sleep than normal persons, and show a heightened physiologic arousal. Personality inventories have disclosed a high incidence of psychologic disturbances in this group, but whether these are cause or effect is not clear.
Furthermore, a category of “conditioned,” or “psychophysiological” insomnia has been denominated, in which a situational trigger for insomnia has ceased, but the sleep disorder persists. Although insomniacs, regardless of the cause, tend to exaggerate the amount of sleep lost, primary insomnia should be recognized as a valid entity.
This common type of insomnia, which is often transitory, can be ascribed to pain or some other recognizable bodily disorder, such as drug or alcohol abuse or, most commonly, to anxiety, worry, or depression. Of the medical disorders conducive to abnormal wakefulness, certain ones stand out—pain in the joints or in the spine, abdominal discomfort from peptic ulcer and carcinoma, pulmonary and cardiovascular insufficiency, and the nocturia engendered by prostatism. The “restless legs” syndrome and periodic leg movements of sleep are not considered in this category and have their own physiology, phenomenology, and treatment as noted below.
Other Causes of Secondary Insomnia
Among the secondary insomnias, those caused by some type of psychologic disturbance are particularly common. Domestic or business worries may keep the patient’s mind in turmoil (situational insomnia). A strange bed or unfamiliar surroundings may prevent drowsiness and sleep. Under these circumstances, the main difficulty is in falling asleep, with a tendency to sleep late in the morning. These facts emphasize that conditioning and environmental factors (social and learned) are normally involved in readying the mind and body for sleep.