There's quite an interesting array of anecdotes here. Mine is a bit different: I was always a night owl, staying up late and sleeping late into the day if left

There's quite an interesting array of anecdotes here. Mine is a bit different: I was always a night owl, staying up late and sleeping late into the day if left to my own devices. In the past couple years that has been completely stood on its head. Now, I regularly collapse into bed around 10 in the evening, and wake up – very reliably – between 5:30 and 6:30 in the morning. I haven't set an alarm in the past two years, except once in a while when I have to get up early for something important. And even then, more often than not, I wake up before the alarm goes off. I am not sure what triggered this change. Perhaps it's age related (I am 66 years old). But really, I have no idea. The change is easy to live with, though, so it doesn't freak me out; but it does make me wonder what happened.