To the best of my knowledge, the intention of a lullaby is to coerce one to sleep. The soundscape is delicate in nature and chooses the instrumentation precisely to achieve its desired result - activating or evoking, whichever you fancy, melatonin.
One then can only assume that a lullaby is playing the role of puppeteer seducing the listener.
Radiohead. Not necessarily a band that creates lullabies, yet one I would often listen to before bed. And as I became intoxicated by the sound I would slowly drift into the abyss of REM cycles until...
a distorted sound, a high pitch, or shrill would enter and awaken me from my slumber leaving me disoriented. Yet, I would continue to listen to them night after night acknowledging that my sleep pattern would be interrupted.
A slight imperfection that added body and depth to an otherwise mundane ritual.
Bliss.
Los Angeles, CA