The Cloudsoul (hún 魂)
It is believed in Traditional Chinese Medicine that the cloudsoul (hún) has an influence on all nocturnal activities, and more peculiarly upon sleep and dreaming. According to the wǔxíng system of correspondences, each phase has a complex series of associations with different aspects of nature; in particular, the cloudsoul is associated with liver-yīn. As a consequence, if liver-yīn is deficient, the hún is deprived of its residence and wanders off at night, causing a restless sleep with many tiring dreams. If liver-yīn is severely depleted, the cloudsoul may even leave the body temporarily at night during or just before sleep.
This brings forth an opportunity for a Celestial Empire/Cthulhu Dreamlands crossover where the player characters are somehow depleted of their liver-yīn (through a yīn-sucking creature?) and find themselves in (possibly a Chinese version of) the Dreamlands. Then they might either stay there and have further adventures in the Dreamlands, or try and find a means to return to the Waking World.