Did you ever notice that you feel sleepy around the same time every day? Constantly running in the background of your brain and body, the circadian rhythm is a built-in 24-hour clock. It guides your body as to when you should be feeling sleepy, as well as when it’s time for your body to feel energized. The circadian rhythm is the built-in smart alarm clock you constantly carry with you, guiding your sleep schedule and daily energy rhythm. Your circadian rhythm works best when you regulate your habits, like going to bed at night when it’s dark and waking up in the morning when it’s light. Naturally, the way evolution configured us.