There is also the "Non-Sleep Deep Rest" (NSDR) technique which seems to be getting some good traction;

1) Non-Sleep Deep Rest (NSDR): Exploring a World Beyond Sleep - https://positivepsychology.com/non-sleep-deep-rest-nsdr/

2) NSDR, Meditation and Breathwork - https://www.hubermanlab.com/topics/nsdr-meditation-and-breat...

3) Neuroscience of Sleep - https://en.wikipedia.org/wiki/Neuroscience_of_sleep