As we emerge from the drowsy holidays with aspirations of being fitter and more productive, one social-media trend jumps out: How about waking up everyday at 5 a.m.? It’s true, some of the world’s top ...

You've probably experienced it—your alarm is set for 6:30 a.m., yet somehow your eyes snap open a few minutes before it goes off. There's no sound, no external cue, just the body somehow knowing it's ...