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 siesta is historically common throughout the Mediterranean and Southern Europe. It is the traditional daytime sleep of Spain and, through Spanish influence, many Hispanic American countries and the Philippines. The word siesta of the Spanish language derives originally from the Latin word hora sexta "sixth hour" (counting from dawn, hence "midday rest"). Siesta is also common in Southern Italy (there called riposo), where museums, churches and shops close during midday so that proprietors can go home for a long lunch and perhaps a snooze during the day’s hottest hours. Einhard's Life of Charlemagne recounts the emperor's summertime siesta: "In summer, after his midday meal, he would eat some fruit and take another drink; then he would remove his shoes and undress completely, just as he did at night, and rest for two or three hours."
The main factors explaining the geographical distribution of the modern siesta are high temperatures and heavy intake of food at the midday meal. Combined, these two factors contribute to the feeling of post-lunch drowsiness. In many countries that observe the siesta, the heat can be unbearable in the early afternoon, making a midday break at home ideal. However, siesta is also practiced in some colder regions, such as Patagonia. This could indicate that the siesta has a stronger relation with culture than with climate.
Biological need for naps
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 notes, "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.
Taking a long lunch break including a nap is common in a number of Mediterranean, tropical, and subtropical countries. The Washington Post of 13 February 2007 reports at length on studies in Greece that indicate that those who nap have less risk of heart attack.
In modern Spain, the midday nap has largely been abandoned during the work week. In southern Spain, mostly in the Andalusian beach villages, siesta is adopted in summer, to avoid the high temperatures of the day, as a way to extend social life till the fresher late evenings, and enjoy holidays with their fiestas.
In the United States, the United Kingdom, and a growing number of other countries, a short sleep has been referred to as a "power nap", a term coined by Cornell University social psychologist James Maas and recognized by other research scientists such as Sara Mednick as well as in the popular press.
Siesta is referred as Vamakukshi in Ayurveda. 
The siesta habit has recently been associated with a 37 percent reduction in coronary mortality, possibly due to reduced cardiovascular stress mediated by daytime sleep (Naska et al., 2007).
Nevertheless, epidemiological studies on the relations between cardiovascular health and siesta have led to conflicting conclusions, possibly because of poor control of moderator variables, such as physical activity. It is possible that people who take a siesta have different physical activity habits, for example waking earlier and scheduling more activity during the morning. Such differences in physical activity may mediate different 24-hour profiles in cardiovascular function. Even if such effects of physical activity can be discounted for explaining the relationship between siesta and cardiovascular health, it is still unknown whether the daytime nap itself, a supine posture or the expectancy of a nap is the most important factor (Zaregarizi, M. 2012).
- Naska, A., Oikonomou, E., Trichopoulou, A., Psaltopoulou, T. and Trichopoulos, D. (2007). Siesta in healthy adults and coronary mortality in the general population. Archives of Internal Medicine, 167, 296-301.
- MohammadReza Zaregarizi, Ben Edwards, Keith George, Yvonne Harrison, Helen Jones and Greg Atkinson. (2007). Acute changes in cardiovascular function during the onset period of daytime sleep: Comparison to lying awake and standing. American J Appl Physiol 103:1332-1338.
- MohammadReza Zaregarizi (Author). Effects of Exercise & Daytime Sleep on Human Haemodynamics: With Focus on Changes in Cardiovascular Function during Daytime Sleep Onset. BOOK, ISBN (978-3-8484-1726-1), March 2012.
- Einhard, Life of Charlemagne, §24.
- Lambert, Craig, PhD (July–August 2005). "Deep into Sleep. While researchers probe sleep's functions, sleep itself is becoming a lost art". Harvard Magazine. Retrieved 25 February 2008.
- Stein, Rob. "Midday Naps Found to Help Fend Off Heart Disease", Washington Post, 13 February 2007, p. A14.
- Maas, James B. (1998) Miracle Sleep Cure: London: Thorsons
- "The National Institute of Mental Health Power Nap Study". 1 July 2002. Retrieved 1 July 2002.
- "Researchers: Power Nap Better than Caffeine to Fight Afternoon Fatigue". Fox News. 4 September 2007.
- "Vamakukshi Ayurvedic Cat Nap"
|Wikimedia Commons has media related to Siesta.|
- Why we could all do with a Siesta – An article about research results from the University of Manchester.
- Is there a decline in Siesta - An article about the decline in siesta.
- Medical disadvantages correlated with Siesta - An article from the Oxford Journal.