I shall make this point clear through a simile. The manufacturer who “attends to business” must, in order to succeed, “concentrate” on a few subjects and exclude all others from his mind. He may for a few hours think of nothing but, let us say, a certain grade of woollens, certain machinery, a certain customer and perhaps a certain engineer and some financial problem connected with those four thoughts. He must therefore exclude from his mind at the time, thoughts of playing golf, buying new clothes, going to the theatre, renting an apartment, repairing his motor car, thoughts of meals, women, card playing, and many other thoughts which are clamouring for admission to consciousness because they all represent human cravings.
In his relaxed moments he will let all those other thoughts come to the surface. Which means that, what tired him, was the fact that he had to keep all those subjects down and allow only the other four to rise to consciousness.
Mental rest consists in admitting ideas pell mell into consciousness without exercising any censorship on them. It consists in passing from a reduced but directed mental activity to an increased but undirected mental activity.
In other words, rest is the free, normal, unimpeded functioning of the vagotonic nerves which upbuild the body and assure the continuance of the race. Ego and sex activities, mental and physical, are constantly struggling for admission to consciousness and for their gratification. They are held down, however, by the sympathetic nerves which play the part of a safety device, moderating or inhibiting the vagotonic activities whenever the latter might endanger the personality.
Physical and mental rest, however, being easily attained through a change of activities, cannot be entirely synonymous with sleep. Sleep takes place mainly while we are resting, although we know of cases when sleep sets in regardless of continued muscular activity, but sleep is not exactly “rest.” We do not sleep because we need rest. In many cases we can or could rest very well, although in such cases sleep is an impossibility.
What then induces sleep? The certainty that we can for a time relax our watch on our environment; a feeling of perfect safety; the conscious or unconscious knowledge that no danger threatens us.
Our receptive contact with reality is attained through the action of our vagotonic nerves which, as stated before, upbuild the body and assure the continuance of the race. Our defensive contact, on the other hand is attained through our sympathetic nerves which interrupt all the activities which are not necessary for fight or flight. As long as some stimulus is interpreted by those nerves as indicating a possible danger, we cannot sleep, although we may, under the influence of terrifying fear, fall into unconsciousness.
A light flashed on our closed lids at night causes us to wake up because sympathetic activities bid us to prepare for an emergency. A light burning evenly in our bedroom and not too bright to cause physical pain, will, on the other hand, allow us to sleep soundly because the constant character of the stimulus does not cause us to expect any danger therefrom.
A mouse rustling a bit of paper will wake us up, but trains passing in front of our window at regular intervals, or the constant rumble of a neighbouring power house will not prove a disturbance as soon as our nerves have learnt to interpret those stimuli as harmless.
Conversation with a dull, witless person, unlikely to best us in debate, puts us to sleep. Argument with keen, sharp-minded people, who keep us on the defensive, may lead to sleeplessness for the rest of the night. A dull book in which nothing happens or is expected to happen, acts as a soporific; we cannot close our eyes before we know the dénouement of a thrilling piece of fiction.