If you're of a certain generation (mine), you probably remember waking up at some ridiculous hour of the morning without even an alarm clock to remind you so you could race to the tv, turn it on, and start watching Saturday Morning Cartoons.
For me, if I remember correctly, Marsupilami started at 6:30 a.m., followed by that show where the kid gets sucked into his Nintendo and has to fight Mother Brain with the help of Kid Icarus and a sentient Game Boy, then Camp Candy (the idea of basing a children's cartoon on "what would happen if John Candy ran a summer camp" creeps me out a bit, in retrospect), then Garfield and Friends (THE BEST ONE -- and it ran for an HOUR), then Teenage Mutant Ninja Turtles.
It seems quaint, now, to think of a world where cartoons were only shown for three hours, one day a week.
At any rate, blah blah blah and I grew up and my circadian rhythms changed and I found it impossible to wake up before 10 a.m. on weekends (and sometimes slept until noon).
Now they've flipped back. Like, overnight.
Part of it, I think, is yoga's fault: if my usual wakeup time is between 5:30 and 6:00 a.m., then of course my body thinks that sleeping until 7:30 is "sleeping in."
But even on these weekend days when I don't get to bed until midnight, when I would think that my body would want to keep me asleep for a little longer, it pops me right up at 7:30 exactly and says "let's go let's go let's go! time to do yogas and write and eat kashi!"
I'd say it was a function of turning almost-thirty, but I've talked to other people in my peer group and they still have no problem sleeping until noon.
I suppose the next step is turning seventy and finding myself compelled to eat dinner at 4 p.m. and go to bed at 9. ^__^