During sleep, there are no adequate reasons for doubting that the flow of our ideas continues as uninterrupted as in a waking state. It is true, that some persons assert that they never dream; and others that they dream occasionally only. But there is a third class, to which I myself belong, who continually dream, and who always, on waking, distinctly discern the fugitive rearguard of their last sleep thoughts. The simplest view of these diversified instances, is to suppose that all persons in sleep are always dreaming, and that the spaces seemingly vacant of dreams, are only gaps in the memory; that all persons asleep always dream, but that all persons do not always remember their dreams.
The suggestive influences that modify the current of ideas in sleep, are not so numerous as those in operation in our waking state.
The principal, indeed in general the exclusive, impulse to our dreaming thoughts, is our past experience and existing character, from and in obedience to which, imagination moulds our dreams.
Not that sensation is suspended in sleep. On the contrary, it appears to have its usual acuteness; and impressions made upon our senses—the feelings produced by an uneasy posture, for instance, or the introduction of sudden light into the room, or a loud and unusual noise, or even whisperings in the ear—will give a new and corresponding direction to the dreaming thoughts. Sensation is only commonly not called into play in sleep: we shut our eyes; we even close the pupils; we cover up our ears; court darkness and quiet; knowing that the more we exclude sensible impressions the better we shall sleep.
But the great difference between sleeping and waking, that which indeed constitutes the essence of the former state, psychically considered, is the suspension of the attention—all the leading phenomena of sleep are directly traceable to this cause: for example—
In sleep we cease to support ourselves, and fall, if we were previously standing or sitting. That is, we cease to attend to the maintenance of our equilibrium. We forget the majority of our dreams: attention is the soul of recollection.
Our dreams are often nonsense, or involve absurdities or ideas which we know to be false. The check of the attention is absent.
Our ideas whirl with unwonted rapidity in our dreams; the fly-wheel of the attention has been taken off.
When we are being overcome with sleep, we are conscious of not being able to fix our attention.
When we would encourage sleep, we endeavour to avoid thoughts which would arouse the attention.