The Conversation discusses factors that influence alertness and brain mechanisms of sleep.

From a sleep science perspective, our alertness levels can be influenced by three factors: time awake, time of day, and time on task. The longer we stay awake, the higher our drive or propensity for sleep (making it easier to fall asleep) and the sleepier we feel. Once sleep is initiated, the propensity for sleep reduces the longer we are asleep.

Our alertness also waxes and wanes across the day and night, reflecting a circadian rhythm. Our lowest alertness level (the nadir) is around 4am, with a second drop in the early afternoon. Most of us have experienced that dozy feeling we get in the mid-afternoon, aptly referred to as the “post-lunch dip”.