In this way, our dream-life touches that childish condition of the intelligence which marks the decadence of old age and the encroachments of mental disease.  The parallelism between dreams and insanity has been pointed out by most writers on the subject.  Kant observed that the madman is a dreamer awake, and more recently Wundt has remarked that, when asleep, we “can experience nearly all the phenomena which meet us in lunatic asylums.”  The grotesqueness of the combinations, the lack of all judgment as to consistency, fitness, and probability, are common characteristics of the short night-dream of the healthy and the long day-dream of the insane.[100]

But one great difference marks off the two domains.  When dreaming, we are still sane, and shall soon prove our sanity.  After all, the dream of the sleeper is corrected, if not so rapidly as the illusion of the healthy waker.  As soon as the familiar stimuli of light and sound set the peripheral sense-organs in activity, and call back the nervous system to its complete round of healthy action, the illusion disappears, and we smile at our alarms and agonies, saying, “Behold, it was a dream!”

On the practical side, the illusions and hallucinations of sleep must be regarded as comparatively harmless.  The sleeper, in healthy conditions of sleep, ceases to be an agent, and the illusions which enthral his brain have no evil practical consequences.  They may, no doubt, as we shall see in a future chapter, occasionally lead to a subsequent confusion of fiction and reality in waking recollection.  But with the exception of this, their worst effect is probably the lingering sense of discomfort which a “nasty dream” sometimes leaves with us, though this may be balanced by the reverberations of happy dream-emotions which sometimes follow us through the day.  And however this be, it is plain that any disadvantages thus arising are more than made good by the consideration that our liability to these nocturnal illusions is connected with the need of that periodic recuperation of the higher nervous structures which is a prime condition of a vigorous intellectual activity, and so of a triumph over illusion during waking life.

For these reasons dreams may properly be classed with the illusions of normal or healthy life, rather than with those of disease.  They certainly lie nearer this region than the very similar illusions of the somnambulist, which with respect to their origin appear to be more distinctly connected with a pathological condition of the nervous system, and which, with respect to their practical consequences may easily prove so disastrous.

After-Dreams.