A siesta (Spanish pronunciation: [ˈsjesta]) is a short nap taken in the early afternoon, often after the midday meal. Such a period of sleep is a common tradition in some countries, particularly those where the weather is warm. The word siesta is Spanish, from the Latin hora sexta - "the sixth hour" (counting from dawn, therefore noon, hence "midday rest").
Factors explaining the geographical distribution are mainly high temperatures and heavy to very heavy intake of food at the midday meal. These two factors combined contribute to the feeling of post-lunch drowsiness. Afternoon sleep is also a common habit in Bangladesh, Bosnia & Herzegovina, China, Croatia, Cyprus, Greece, India, Iran, Italy (southern), FYROM, Malta, Montenegro, North Africa, the Philippines, Serbia, Slovenia,and Vietnam. In these countries, the heat can be unbearable in the early afternoon, making a midday break at home ideal. In many areas with this habit, it is common to have the largest meal of the day in the very early afternoon, as is practical and common in farming.
The original concept of a siesta seems to have been merely that of a midday break intended to allow people to spend time with their friends and family. It has been suggested that the long length of the modern siesta dates back to the Spanish Civil War, when poverty resulted in many Spaniards working multiple jobs at irregular hours, pushing back meals to later in the afternoon and evening. However, this hypothesis sounds unlikely, considering that the siesta tradition was very common in Latin America and other countries with Hispanic influence, much before the Spanish Civil War.
Siesta takes place when the Sun is at its highest point, this is when the Sun's ultraviolet radiation is at its peak at midday. Prolonged exposure to ultraviolet radiation may result in sunburn, especially if one has fair skin. Recurring overexposure to ultraviolet radiation can cause some forms of skin cancer.
The Sun's infrared radiation causes high air temperatures from the midday onwards, the highest temperatures taking place in the early afternoon. High temperatures can cause fatigue or in a more serious case heat exhaustion or hyperthermia (sunstroke).
Older, pre-teenage children are usually incapable of napping, but acquire the ability to nap as teenagers.
The timing of sleep in humans depends upon a balance between homeostatic sleep propensity, the need for sleep as a function of the amount of time elapsed since the last adequate sleep episode, and circadian rhythms which determine the ideal timing of a correctly structured and restorative sleep episode. The homeostatic pressure to sleep starts growing upon awakening. The circadian signal for wakefulness starts building in the (late) afternoon. As Harvard professor of sleep medicine Charles A. Czeisler claims, "The circadian system is set up in a beautiful way to override the homeostatic drive for sleep."
Thus, in many people, there is a dip when the drive for sleep has been building for hours and the drive for wakefulness has not yet started. This is, again quoting Czeisler, "a great time for a nap." The drive for wakefulness intensifies through the evening, making it difficult to get to sleep 2–3 hours before one's usual bedtime when the wake maintenance zone ends.
In some individuals, postprandial dip, a brief drop in blood glucose levels caused by the body's normal insulin response to a heavy meal, may produce drowsiness after the meal that can encourage a nap. However, the appearance of the dip is primarily circadian as it occurs also in the absence of the meal.
The concept of a midday nap is also prominent in other tropical or subtropical countries, where the afternoon heat dramatically reduces work productivity. The Washington Post of February 13, 2007 reports at length on studies in Greece that indicate that those who nap have less risk of heart attack.
An example of a siesta-like habit can for example be found in Serbia and Slovenia. Especially among older citizens, it is common to observe the so-called 'house rule', requiring people to refrain from telephoning or visiting each other between 14h and 17h, as people are supposed to be resting; especially since lunch in Serbia and Slovenia, eaten usually between 13h and 14h, is the main dish of the day. In some southern German-speaking regions, the Mittagspause de:Mittagspause or Mittagsruhe de:Mittagsruhe is still customary; shops close, and children are expected to play quietly indoors.
In South Asia, the idea of a post-lunch nap is common, and the idea of going to sleep after a light massage with mustard oil to induce drowsiness was very popular before industrialization. It was also very popular to consume a light snack during this ritual; it was thought that this practice would make one a better person. In Bangladesh and West Bengal, the word which describes the concept is bhat-ghum, literally meaning "rice-sleep", a nap after lunch.
Afternoon sleep is also a common habit in China and Taiwan after the midday meal. This is called '"wujiao" in Chinese. Almost all schools in Mainland China and Taiwan have a half-hour nap period right after lunch. This is a time when all lights are out and one is not allowed to do anything other than rest or sleep.
Some Japanese offices have special rooms known as napping rooms for their workers to take a nap during lunch break or after overtime work.