Wikipedia on board: Segmented sleep, also known as divided sleep, bimodal sleep pattern, bifurcated sleep, or interrupted sleep, is a polyphasic or biphasic sleep pattern where two or more periods of sleep are punctuated by periods of wakefulness. Along with a nap (siesta) in the day, it has been argued that this is the natural pattern of human sleep. A case has been made that maintaining such a sleep pattern may be important in regulating stress.
--- In firstname.lastname@example.org, terry foreman <terry.foreman@...> wrote:
> 'Dreamland': Open Your Eyes To The Science Of Sleep
> by Maureen Corrigan <http://www.npr.org/people/4529709/maureen-corrigan>
> "One particularly fascinating sleep fact that [the author of *Dreamland*]
> reports is that the sleep rhythms of the human brain have fundamentally
> changed over the centuries. Medieval literary texts, medical manuscripts
> and tales make reference to a mysterious "first sleep" and "second sleep."
> The "first sleep" began shortly after sundown and lasted until after
> midnight. When people woke up, they would pray, read, have sex, whatever.
> The "second sleep" then lasted until sunup. In experiments, researchers
> have found that when people live solely by natural light, they revert back
> to this ancient "segmented sleep" pattern and that, chemically, the body in
> that interval between first and second sleep is "in a state equivalent to
> what you might feel after spending a day at the spa." It seems that, thanks
> to the light bulb, the entire industrialized world is sleeping unnaturally."