The nap is the keystone of the chronobiological balance of sleep.
It must not contribute to conceal a pathological excessive sleepiness.
It is a powerful (double edged) weapon that has to be handled with care because the need to sleep in the start of the afternoon is physiological for some but pathological in others.
Be careful! The practice of the nap must not conceal a pathological sleepiness.
The nap in a subject who suffers of overweight and hypertension must lead to a systematic investigation of a sleep apnea syndrome.
"Sleep and general medicine" dedicates three articles to the nap :
«Siesta : time that is given to sleep, during the warmest part of the day...» (Émile Littré, Dictionary of the French language, 1863-1872).
From the Latin sexta hora, the sixth hour, which corresponded to the middle of the day, noon, for the Romans (the first hour being that of sunrise).
That deliberate episode of sleep possesses beneficial powers known since the start of mankind. It is therefor a "sleep that heals" but the discovery of a sleep descrived as REM sleep in the 50’s (by the Pr. M. Jouvet in Lyon and Pr. W. Dement in the United States) and that of internal rythms (1962, out of time speleological experiments of Michel Siffre  ) have given the nap a true dimension of a medication.
Like for aspirin, that "somnications" doesn’t have the same effect whether it is administered in very small doses close in time (15 minutes every two hours like for solitary navigators) or, on the contrary,"on demand", at "a strong dose" or even at a "massive dose" (like tennagers readily do on Sundays).
The word "nap" covers very different concepts according to the schedule, the duration and the circumstances of occurrence of the sleep episode.
In the absence of somnological knowledge, since everybody has different needs (and intakes) of sleep and since everybody sees (in this context more than anywhere else) is persuaded to know better, how should this question be answered :
Are two sleeps more valuable than one ?
In this study (made with soldiers, presented by Pr Jouvet), the collapse of the performances and vigilance over four days without sleep has been measured.
The circadian variations of the two curves linked to the cycle of the temperature and their change as the days go by can be seen easily.
Above all, note the spectacular speed of recovery on the 4th day, after only 3 hours of sleep and without that we know exactly why !
For a long time, the practice of the nap has been considered as abnormal. It was reserved for the children, the old people and the sick persons.
And the sleepy subjects suffered secretly in order not to appear like lazy people to the eyes of the "normal" people...
An opposite tendency develops itself nowadays, in response to the problems of excessive daytime sleepiness that we encounter in modern societies.
The sleep doctors and the authorities, sensible to the statistics of (traffic, work....) accidents, have "communicated" a lot on the theme of: "The nap is a good habit".
And the insomniac subjects who have heard that "it was necessary to have naps" maintain a true vicious circle.
.. while the sleep problematics (tiredness, insomnia, sleepiness) are in constantly getting worse in modern societies.
"Sommeil-mg" wishes to contribute to promote useful knowledge for a rational use of the nap :
The neophyte reader can usefully refer to the document "Didal of the private individual" which is more concise, and designed for the general public.
In what cases and how to use that "somnication ? Which are its undesirable effects? What are its contraindications?
 Michel Siffre (young speleologist of 22, from Nice) first wants to try to survive in a hostile environment (in the underground glacier of the gorge of Scarasson, at 2000 m of altitude in the southern Alps), then he completes his project with the study of the "loss of the sense of time" : he decides not to take any watch with him in order to retrieve "man’s original rythm". It is the first experience of long time isolation in man. Back to text