My father taught me an "instasleep" system that may(?) be related: basically you start distally and work proximally, becoming aware of any tension in body parts and allowing them to relax. When I do it I feel "myself" kind of "diffusing" to meet my environment, like fresh and salt water meeting to form a brackish zone, sometimes with a rocking sensation, and I usually fall asleep well before getting to core muscles. (when I was younger, people used to ask "how can you fall asleep on rocks?" to which I replied "you have to choose the comfortable ones", but it was likely more this technique)

The oddest thing about this technique is the source: although it sounds very Baba Cool, he'd been taught it in Uncle Sam's service.