Understanding Sleep and Circadian Systems

Circadian systems, or rhythms, may sound complex, but it really is all about gaining an understanding of how your own body works so that you maximize the odds that you will be able to get a good night’s sleep naturally.

Simply put, circadian rhythms are the physical, mental, and behavioral changes that happen in your body every 24 hours. Getting a handle on how they function can help you get the rest you need, which is necessary for your physical, mental, and emotional health.

The quality and length of your sleep are related to two particular systems—“Process C” [circadian] and “Process S” [sleep], explains Melissa Knauert, MD, PhD, a Yale Medicine pulmonary, critical care, and sleep medicine specialist.

From the time you wake up until you go back to sleep at bedtime, your body slowly accumulates “more and more sleepiness,” Dr. Knauert says. “And every day, combatting that is the circadian drive [Process C], which we also call the ‘awake drive.’ When you start in the morning, your circadian drive is essentially off, and then it slowly builds throughout the day to make you more and more awake to balance out that sleepiness.”

It's natural to experience energy dips in the afternoon, but people don’t usually go to sleep until the circadian system turns off, right before bedtime and stops alerting you to be awake, Dr. Knauert explains.

“All of a sudden, you have this unopposed sleepiness and feel very tired. We call this the sleep gate or sleep pressure [Process S], which allows us to go to sleep,” Dr. Knauert says. “And at night, the circadian system stays off as you continue to sleep.”

In this video, Dr. Knauert discusses circadian systems and how you can play around with yours to get optimal rest.