Thanks for the reference. (I actually DID do a search for “dark circles” in the GQ board before I posted and it came up with nothing)
Still, the thread doesn’t seem to entirely answer the question (at least to my satisfaction). The statement that dark circles are not an indicator of lack of sleep seem ridiculous to me. I’m not really persuaded by any of the other suggestions either (skin sag? sinuses? - why when I’m TIRED?)