hypnagogic

1. Inducing sleep; soporific.
2. Of, relating to, or occurring in the state of intermediate consciousness preceding sleep: hypnagogic hallucinations.

[French hypnagogique : Greek hupnos, sleep; see hypno- + Greek agōgos, leading (from agein, to lead).]

1. Inducing sleep; soporific.
2. Of or relating to the state of drowsiness preceding sleep.
3. Relating to the images or hallucinations sometimes perceived during this state.

Producing sleep.

The adjective has one meaning:

Meaning #1: sleep inducing
  Synonyms: soporific, soporiferous, somniferous, somnific, hypnogogic