Peaks and troughs in the body's Melatonin production during the circadian (sleep) cycle represented in a 24-hour period.
<a href="//commons.wikimedia.org/wiki/User:Rechargeenergy" title="User:Rechargeenergy">Rechargeenergy</a>
CC BY-SA 4.0
<span class="int-own-work" lang="en">Own work</span>