The hypnoidal state into which man is apt to fall so easily, is well adapted to fear suggestions, since the fear instinct and the impulse of self-preservation are present in the subconsciousness, exposed during trance states to all sorts of fear suggestions and superstitions. It is during these brief periods of primitive hypnoidal states that the animal is exposed to attacks of enemies whose senses become sharpened to detect the weak spots in the armor of their victims, immersed in the momentary rest of the hypnoidal state. During these periods of repose and passivity or of sleep stage, the animal can only protect itself by all kinds of subterfuges, such as hiding in various inaccessible places, or taking its rest-periods in shady nooks and corners, or in the darkness of the night. Each hypnoidal period closely corresponds to the larval stage of the insect, reposing in its cocoon,--the most critical time of the insect organism, most exposed to the depredations of its enemies. And still the hypnoidal state is requisite to the animal in order to restitute its living matter and energy which have been wasted during the active moments of its life activities. Hence the weakness of the animal depends on the very constitution of its organism. The hypnoidal state, although absolutely necessary in the process of metabolism, is also the moment of its greatest danger, and the fear instinct is specially intense at the onset of that hypnoidal moment, the lowest point of the weakness of the organism. The animal, after taking all precautions, is finally paralyzed into temporary immobility at the risk of its own existence. The fear instinct determines the nature and character of rest and sleep. The lower the animal, the scantier are its means of defense in the ceaseless struggle for its preservation. The simpler the animal, the greater and more numerous are the dangers menacing it with total extinction,--hence it must be constantly on its guard. A state of sleep such as found in the higher animals is rendered impossible. The sleep must be light, and in snatches, rapidly passing from rest into waking,--the characteristic of the hypnoidal state. The fear instinct is the controlling factor of sleep and rest. When we are in danger the sleep is light and in snatches, and we thus once more revert to an ancient form of rest and sleep. _The insomnia found in cases of neurosis is a reversion to primitive rest-states, found in the lower animals._ The insomnia is due to the fear instinct which keeps dominating the conscious and subconscious mental activities, a state which has prevailed in the early stages of animal life. That is why the sleep of neurotics is unrefreshing and full of dreams of dangers and accidents, and peopled with visions of a terrorizing nature. Hence the neurotic fear of insomnia which is itself the consequence of the obsession, conscious and subconscious, of the fear instinct.