How much sleep do we need? This is a question that cannot be answered arbitrarily as applying in all cases. Individuals differ. Without doubt, some require more sleep than others.
Thomas A. Edison, who is an extraordinary man, not only in respect to his vitality but in every other characteristic as well, has frequently been quoted as saying that most men and women sleep too much. Mr. Edison himself claims to maintain the best of health with from three to five hours' sleep out of every twenty-four. We have heard of other cases too, of men and women with exceptional vitality, who have seemed to thrive on four or five hours' sleep. It is possible that this small allowance of sleep may be sufficient in such cases, but if so, it is undoubtedly due to the exceptionally powerful organism which these particular persons have inherited.
No definite rule can be laid down as to the amount of sleep required by different individuals, for those possessing the greatest amount of vitality and the strongest organisms will require less sleep than those of limited vitality and weak functional powers. Those possessing a strong functional system and great vitality are able to build up energy during sleep and recuperate from the exertions of the preceding day more rapidly than can those less favored in this respect. In other words, a very strong man can be quickly rested. His system can more rapidly than that of a weak man repair the wear and tear of his daily work. The man or woman with limited strength and a less vigorous functional system would require a longer time in which to recuperate. Therefore, what would hold good in the case of such an extraordinary man as Mr. Edison cannot be depended upon in the case of the average man or woman, and certainly will not meet the needs of those who are debilitated and striving to build vitality.
Generally speaking, therefore, I maintain that most people at the present day sleep too little rather than too much. I would not stipulate any special number of hours for sleeping but I would advise everyone to secure as much sleep as he requires. It has often been said that if you sleep too much you will be stupid as a result. Such results are usually brought about by sleeping in unsatisfactory environment, particularly in stuffy rooms in which the air is vitiated and really unfit to breathe. I cannot imagine one feeling stupid as a result of oversleeping when sleeping out-of-doors, or when the supply of air is absolutely fresh. Excessive heat would probably be conducive to restlessness, but this is purely a detail which I shall take up later. Under natural and healthful conditions one will rarely sleep too much. If you sleep until you wake up naturally there is little danger of your sleeping too much. Without doubt most people need from seven to eight hours' sleep; some of them need more, particularly women and children, who in many cases require from nine to ten hours' sleep or even more. These are general statements. Individual exceptions will be many, but, as I have said, it will be found that those who need less sleep are men and women of extraordinary vitality.
The quality of sleep is really more important than the duration of sleep. It is quality or depth of sleep that is really what counts, and to secure this it is necessary that certain healthful conditions be observed. The first of these is a normal condition of physical or muscular fatigue. This is easily distinguished from nervous fatigue or exhaustion in which the entire system is more or less upset. Abnormal states of this sort arise from excitement, excessive mental work, or other conditions involving severe nerve strain. This nervous fatigue is not usually conducive to sleep, but a tired condition of the muscles of the body generally, as a result of natural physical activity, is always favorable to sleep. Many who complain of insomnia, therefore, would often be able to remedy their trouble by the simple expedient of a long walk, covering sufficient distance to bring about the physical fatigue which makes sleep possible. Conditions of air, temperature and bed covering are also important factors in connection with the quality of sleep.
If you are a sound sleeper it may be possible for you to secure more benefit from three to four hours' sleep than a shallow sleeper may secure in eight hours of a lighter degree of sleep. This extreme depth of sleep means complete rest for the brain, absolute loss of consciousness, and, to a certain extent, loss of sensibility in respect to our senses. In the lighter degree of sleep certain parts of the brain may be at rest, while others are more or less active. Dreaming represents a state of partial consciousness rather than a condition of complete rest, inasmuch as various parts of the brain are active. One may thus be conscious of his dreams. There is no doubt, however, that in other cases various parts of the brain may be active though we may not be conscious of their activity. We have all heard of instances where mathematical problems appear to have been worked out during sleep, and we have heard of musical compositions and poems being produced during sleep. All these phenomena represent a condition in which one is partly asleep and partly awake; in other words, some parts of the brain are active and others are asleep. In extreme depth of sleep when all the mental faculties are at rest, the energies are relaxed, and the activities of the body are at a low ebb; it is such sound sleep that makes for rapid recuperation. The deepest sleep generally occurs within the first few hours after falling to sleep, and it gradually becomes lighter and lighter in degree until consciousness is reached. Dreams, therefore, represent partial consciousness and usually appear in the earlier hours of the morning. When one states that he dreams all night he is invariably mistaken. One may seem to live over periods of days and even years in a dream, the actual duration of which may be measured in minutes. The chances are that the dreamer enjoyed a sound sleep before his dreaming commenced.
Although I have said that depth of sleep is more important than the duration of sleep, yet it is true that when one sleeps very soundly he usually sleeps longer. In other words, when one reaches great depth of sleep the transition to the period of wakefulness is only gradual, and it requires a longer time to complete the sleep and wake up than it would if one did not sleep so deeply, or, as we would say, so soundly. It will be found that healthy children, who unquestionably sleep very soundly, also sleep for many hours at a time. They may have dreams but these occur in the later hours of sleep, as every mother has observed. The man or woman well advanced in years who can secure the same depth of sleep that a vigorous child en joys will undoubtedly spend the bigger part of the night in sleep and will acquire exceptional vitality as a result.
Bodily rest, even without sleep, is undoubtedly of great value for purposes of recuperation. To a certain extent such rest, especially if associated with a state of very complete relaxation of the muscles, will make it possible to take less sleep without serious devitalizing results. The man or woman who suffers from insomnia should learn that he can recuperate to a considerable extent through simple physical relaxation without the unconsciousness of sleep. Undoubtedly the physical inactivity common among civilized races has much to do with their ability to keep late hours. But of course this involves more or less nerve strain. The brain does not get sufficient rest, and the loss of sleep involves such an expenditure of energy through the brain as to constitute a serious drain upon the nervous system. Even though rest for the body during consciousness is of certain value, it cannot go very far in taking the place of true sleep. To the higher centers of the brain and nervous system an opportunity must be given for the complete relaxation that comes only with the entire loss of consciousness.
As I have already said, those who are lacking in vitality and who are trying to build strength need more sleep than those who are already strong. Especially those who find it difficult to sleep need additional nervous strength and should carefully observes rules that will promote sleep. One will often hear sufferers from insomnia complain that they never sleep! They are convinced that night after night and week after week passes without their being able to close their eyes in slumber. They are deluded in every case, because they could not maintain life for more than five or six days if this were true. The fact is that they drop off to sleep and then awaken without being conscious that they have been asleep. At the same time, in all such conditions, it is necessary to improve the quality of sleep so that it will be truly refreshing. I have already referred to the influence of good healthy muscular fatigue as a means of enabling one to sleep. Walking and out-of-door life will in almost every case make the nervous man or woman sleep like a child. One should not be too fatigued, but sufficiently so to thoroughly enjoy the sensation of lying down. One cannot truly enjoy sleep except when he has reached this condition of bodily fatigue. To induce this, I would recommend a walk in the evening before going to bed, covering several miles. Although walking for health should ordinarily be brisk enough to stimulate breathing and arouse an active circulation, thus strengthening the internal organs, for the purpose of promoting drowsiness the last mile or two of the evening walk should preferably be very slow. Fast movements are stimulating to mind and nerves. Slow movements have a sedative effect. By walking very slowly as if one were tired the desired effect of fatigue is more satisfactorily secured. One imagines the need of rest under such conditions.
The quality of the air is another important factor, though I need not dwell upon that here. The air you breathe during sleep should be especially fresh and pure, particularly so because of the more shallow character of the breathing. If you are in a room, all the windows should be open as wide as possible. If you have a covered balcony or porch, or if you can avail yourself of a flat roof, it is always advisable to sleep out-of-doors. The increased vitality will more than repay you for your trouble. There is something about out-of-door sleeping that vitalizes, energizes, and refreshes one to an unusual extent.