Someone accidentally hit the hibernation button

I wasn't up late. I hadn't had a heavy meal or alcohol. I'd had a good siesta in the afternoon. But I slept very deeply. And long.

I roused to consciousness in the wee hours enough to see it was 4:26. I rolled over and went back to sleep.

I woke later, thinking it might be about 7:00, because that's how it usually goes. It was 9:04.

What? How did that happen? Not that I'm complaining. It caused no schedule problems (since I don't have a schedule) and I feel fine. It's just a small mystery.