Hypnagogia, also referred to as "hypnagogic hallucinations", is the experience of the transitional state from wakefulness to sleep: the hypnagogic state of consciousness, during the onset of sleep (for the transitional state from sleep to wakefulness see hypnopompic). Mental phenomena that may occur during this "threshold consciousness" phase include hallucinations, lucid thought, lucid dreaming, and sleep paralysis.

Matej Vojtus
Source: Hypnagogia