Immediately before dropping off to sleep and immediately after awakening (but prior to full wakefulness) we are in a state of mind in which we are peculiarly susceptible to certain kinds of vivid hallucinations, usually visual or auditory in nature. Many people have had, for example, the experience of imagining that they have risen from bed only to emerge into full awareness and find themselves still prone. Most everyone has also experienced brief visual or auditory illusions when they were fatigued owing to excessive lack of sleep or overexertion. The technical name that British researcher Frederick Myers gave these experiences is hypnagogic, and the state of mind that accompanies them is referred to as a hypnagogic state.
When falling off to sleep, according to Myers, the brain “produces steady alpha rhythms” that induce the sleeper into full relaxation. When the alpha rhythms break up, Stage 1 sleep is fully realized and the sleeper begins to enter the dream state. The initial hypnagogic “visions” include “formless shapes such as waves of pure color” and often include distorted faces and archetypal images.
Recent research into hypnagogic states suggests that these visions occur when, due to the “rapid change in consciousness” the mind is struggling to gain control.