> I’ve found something similar: to fall asleep visualise something vividly. It could be a scenario (a daydream as you suggest) or a scene.
This method also has the advantage for those of us who can't normally visualise while awake. When you are on the boundary of sleep you can somehow take advantage of your dream circuits to help you out. This is the only time of day I'm able to see anything but black when closing my eyes.
The steps go something like this: be still, relax face, stop thinking (or distract self with audio you’re heard before), vividly picture, wake up.