Siesta

It is very common here in Egypt, unlike in the West, if you phone someone in the middle of the afternoon, you will wake them up. It is well known that it is not a good time to visit people during this time for the same reason. Families will stay awake together until the early hours of the morning, and will think nothing of calling their friends at 1.00 or 2.00 am to have a chat.

Siesta
A siesta (IPA: [siˈɛstə], original Spanish pronunciation ['sjest̪a]) is a short nap taken in the early afternoon, often after the midday meal. Such a period of sleep is a common tradition in hot countries. The word siesta is Spanish, from the Latin HORA SEXTA - "the sixth hour" (counting from dawn, therefore noon, hence "midday rest").

The siesta is the traditional daily sleep of the Southern region of Alentejo, in Portugal, known as sesta. It was adopted also by the Spanish and, through European influence, by Latin American countries and the Philippines. Afternoon sleep is also a common habit in China, India, Italy ("riposo" in Italian), Greece, Malta, The Middle East and North Africa . In these countries, the heat can be unbearable in the early afternoon, making a midday break in the comfort of one's home ideal. However, in some countries where naps are taken, such as Northern Spain, Southern Argentina, and Chile, the climate is similar to that of Canada and Northern Europe. Besides the climate, in many countries with this habit it is common to have the largest meal of the day in the afternoon, in contrast with other countries where only a lighter lunch is taken. Thus, a siesta may also be a natural result of this large meal...

Biological need for naps

In recent years, studies have suggested a biological need for afternoon naps. The body is on a 24-hour body clock, which makes you wind down between 1 a.m. and 6 a.m. and again in the three hours directly after lunch. Researchers found that subjects of the studies felt that it was easiest to fall asleep at night and in the afternoon.[2]

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.The behaviour is also common in tropical medical schools where students like to take a nap after the morning classes in the afternoon. It serves as a preparation for trans night study or simply called 'tranzi'.
Wiki source