Branislav Nikolic wakes up every morning at 7 a.m., energized and ready to greet the day, no alarm clock required. At night, instead of doom-scrolling until 2 a.m., he's peacefully asleep by 11:30 p.m. It's been his routine for the past decade, thanks to his fascination with circadian rhythm, the body's internal clocks that regulate energy and appetite.