Many people have a temporary drop in alertness in the early afternoon, commonly known as the "post-lunch dip." While a large meal can make a person feel sleepy, the post-lunch dip is mostly an effect of the circadian clock. People naturally feel most sleepy at two times of the day about 12 hours apart—for example, at 2:00 . and 2:00 . At those two times, the body clock "kicks in." At about 2 . (14:00), it overrides the homeostatic buildup of sleep debt, allowing several more hours of wakefulness. At about 2 . (02:00), with the daily sleep debt paid off, it "kicks in" again to ensure a few more hours of sleep.