Insomnia; and Other Disorders of Sleep is a work by Henry M. Lyman.

It delves into topics such as the nature and cause of sleep, insomnia or wakefulness, the remedies for insomnia and dreams and somnambulism. Involuntary act of memory was really the idea of association suggested by the book.

This had unconsciously aroused the apparatus of association in the brain, and the particular scene thus brought before the mind had been further suggested by the circumstance that the last object, external to the printed page, upon which I had fixed my attention, was a large ship, lying in the river, near the bridge, just crossed by the car in which I rode. Numerous other examples of a similar character might be related to illustrate the fact that the brain is a reservoir of sensory impressions, some of which, at the moment of their original incidence, have aroused the mind to a greater or less degree of conscious attention, and have then all lapsed into a latent or potential condition.

But, though latent, they are none the less persistent, and only await the suppression of other inhibitory forces to become once more capable of arousing attention. Such inhibitory impulses are continually furnished by the action of the sensory organs on the one hand, and by the energy of the mind upon the other.

So soon, therefore, as the organs of sense and of voluntary impulse are sealed with sleep, if the remaining portions of the brain are still operative, and are left to their own unrestrained activity, a more or less disorderly series of ideas occupies the mind. .