I usually wake up just ahead of my alarm. What's up with that?

Humans have an elegant and intricate system of internal processes that help our bodies keep time, with exposure to sunlight, caffeine and meal timing all playing a role. But that doesn't account for "precision waking." (Sarah Mosquera/NPR)

Maybe this happens to you sometimes, too:

You go to bed with some morning obligation on your mind, maybe a flight to catch or an important meeting. The next morning, you wake up on your own and discover you've beat your alarm clock by just a minute or two.