A nap is a short period of sleep taken outside of the normal sleep period (i.e. usually during the daytime). In most Western countries, naps are generally associated with young children and the elderly, but in many cultures – especially in hot climates – it is a widely accepted part of the normal day. A daytime nap is an established habit in many Mediterranean countries, and naps are also common in parts of Africa and China. The Japanese inemuri (a nap taken at work in order to increase productivity and demonstrate professional commitment) has a whole ideology built up around it.
Spain is perhaps the country most identified with naps, and historically it has raised the siesta almost to the level of an art-form. The daily siesta used to be a sacrosanct practice, and an integral part of the Spanish lifestyle, which typically involved late-night food and dancing. In the hustle and bustle of modern Spain, however, it is much less ubiquitous than it used to be. Typically, people no longer live close enough to their work to go home for a nap, and they are more likely to take a long (and probably liquid) lunch instead, and then still go out to eat and drink until the early morning hours. Unfortunately, this is not a sustainable way of life and, as a result of sleep deprivation, Spain now has one of the highest accident rates and lowest productivity in Europe.
Naps often coincide with the temporary drop in alertness most people experience in the early afternoon, commonly referred to as the “post-lunch dip”. This is actually more a function of the biological or circadian clock than any reaction to having eaten, although lunch foods rich in carbohydrates may also increase levels of tryptophan in the brain which encourages sleepiness. The post-lunch dip is built into the body’s circadian rhythm, to the extent that some scientists believe that we are naturally biphasic, i.e. designed to take two sleep periods, a long one at night and a short one in the early afternoon.
Statistics show that we are naturally less alert and more prone to microsleeps (“nodding off”) during this post-lunch dip in the early afternoon. For example, up to 25% of road accidents are caused by microsleeps, and we are three times more likely to fall asleep at the wheel at 2pm than we are 6pm. A short planned nap of 15 to 20 minutes may increase alertness and motor skills for up to 2-3 hours during this dangerous time. It is also claimed that naps can significantly improve learning and memory recall, with some studies claiming quite dramatic results. Some studies even claim that, over an extended period, a regular afternoon nap can lower blood pressure and improve cardiovascular health, although the validity of these conclusions are perhaps more debatable.
Sleep during naps is typically not long or deep enough to provide the restorative benefits of nighttime sleep, and should not normally be used as an alternative, particularly for people suffering from clinical insomnia or depression. However, a short “power nap” or “cat-nap” of 10-20 minutes may have some beneficial effects, provided the nap is curtailed before stage 3 slow-wave sleep (entering deep sleep and failing to complete the full sleep cycle is usually associated with the grogginess and disorientation of sleep inertia and, as a result, the napper may feel even worse than before the nap). Interestingly, this sleep inertia after a nap can be avoided to some extent by taking caffeine just before the nap: the 20 minute lag in the effects of the caffeine should not interfere with getting to sleep and, by the time it does become active, it is “ready” to counter the sleep inertia on awakening.
“Extreme napping”, sometimes called a polyphasic sleep pattern, involves taking regularly planned short naps (e.g. 15 minute naps every 4 hours) in place of a single long nighttime sleep period. While the practice has had a certain amount of anecdotal success – Leonardo da Vinci supposedly adopted a polyphasic sleep regime, as did Buckminster Fuller for a time – it is generally regarded as a passing fad, and most serious studies have concluded that such a practice is stressful, unsustainable and often positively harmful (both physically and psychologically). While the vast majority of mammals are naturally polyphasic sleepers, humans are among the 15% or so of naturally monophasic sleepers.
Microsleeps are short, involuntary periods of sleep, lasting from a fraction of a second to thirty seconds, usually resulting from sleep deprivation or mental fatigue, or from some kind of sleep disorder. They may be accompanied by head nodding, drooping eyelids, etc, or they may occur with little or no warning, and often the sufferer may be completely unaware of having slept. This can obviously be very dangerous in situations requiring constant attention, such as driving a vehicle or operating machinery.