I often feel like I’ve spent the night inside a rotating drum in the mornings, but I don’t think that’s what they mean.
[I think this is related but if it seems too off-topic then please report to moderators so this post can be deleted] The TV program NOVA had a recent episode all about sleep and I think it mentioned this. https://www.pbs.org/wgbh/nova/video/mysteries-of-sleep/ The part about "pink noise" being played during sleep to help get better sleep was very interesting. I don't know whether the video is restricted by region but there's also a transcript.
