Some involuntary muscle twitching is normal as a person falls asleep, and this type of jerking is called hypnagogic myoclonus.
Hypnagogic hallucinations, intense and sometimes terrifying experiences that occur as the person is falling asleep.
In these respects, and in the awakeness of the scryer, crystal pictures differ from hypnagogic illusions.
People who cannot scry may have these hypnagogic illusions, and, so far, may partly understand the experience of the scryer who is wide awake.
Occasionally, in hypnagogic illusions, the observer can see the picture develop rapidly out of a blot of light or colour, beheld by the closed eyes.