We insist on using the terms normal waking life, for there are forms of abnormal waking life in which attention is withdrawn as completely from reality as it is in normal sleep.
In the disease designated by psychiatrists as dementia praecox, the patient may become entirely negative, some time regressing to the level of the unborn child, and withdraw even more entirely from reality than the sleeper who, without awaking, is conscious of certain stimuli and performs certain actions showing a comprehension of their nature.
CHAPTER II: FATIGUE AND REST
What causes sleep? What causes us to withdraw partly our attention from our environment? The answer: brain anaemia, is unsatisfactory for we may ask in turn: what causes brain anaemia?
A study of brain anaemia leads one to conclude that it coincides with the usual sleeping period and that it is produced by sleep instead of producing sleep.
The large majority of laymen and scientists, however, give a much simpler answer: we go to sleep because we are tired and need rest.
Even as sleep and death have been coupled in the literature of all nations, fatigue and sleepiness, rest and sleep have come to be generally considered as synonymous.
Fatigue, however, is as difficult to define scientifically as sleep. Drawing a line between physical fatigue and mental fatigue does not simplify the problem; on the contrary, it complicates it by positing it wrongly.