hypnagogic
That induces sleep; soporific, somniferous.
That accompanies falling asleep; especially, pertaining to the semi-conscious period immediately preceding sleep.
But if we are in the right mood, a second of such lethargy is enough to make a hypnagogic [translating hypnagogische] hallucination appear, after which perhaps we reawaken, until the oft-repeated performance is brought to an end by sleep.
Where it comes from
From French hypnagogique, from Ancient Greek ὕπνος (húpnos, “sleep”) + ἀγωγός (agōgós, “leading”).
Adapted from the Wiktionary entry hypnagogic (CC BY-SA 4.0).