An afternoon dip in energy level is a commonly observed phenomenon in society and is also known as post-lunch dip.
Once awake, performance should be rather constant over the day, but frequently one may experience a dip in energy level and performance in the afternoon. This dip is also referred to as the post-lunch dip. Timing of the post-lunch dip is often between 2 and 4 pm and a shortage of night time sleep seems to trigger its occurrence, especially in young people. Although a heavy lunch may worsen the feelings of afternoon sleepiness, the post-lunch dip may also occur without a preceding meal. Its occurrence is thought to be generated by the natural sleep-wake processes itself.