The answer resides with your twenty-four-hour circadian rhythm, which offers a brief period of salvation from sleepiness. Unlike sleep pressure, your circadian rhythm pays no attention to whether you are asleep or awake. Its slow, rhythmic countenance continues to fall and rise strictly on the basis of what time of night or day it is. No matter what state of adenosine sleepiness pressure exists within the brain, the twenty-four-hour circadian rhythm cycles on as per usual, oblivious to your ongoing lack of sleep.
