From an NPR program:
One particularly fascinating sleep fact that Randall 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.
From the Globe and Mail (Montreal):
“The magazine cites research, including a paper by historian Roger Ekirch at Virginia Tech, who after 16 years of study found a bundle of evidence – in diaries, court documents and literature – that humans naturally used to divide their sleep in two, often waking up in the middle for a couple hours. In the middle wake-up, Dr. Ekirch reports, people might stay in bed, read or write, go out and visit neighbours, or even partake in some middle-of-the-night canoodling. (The research uncovered a doctor’s manual from 16th-century France that recommended couples trying to conceive had the best chance between after the ‘first sleep,’ as it was called.) In the 19th century, the notion of the first and second sleep began to lose favour, and by the 1920s, the pattern had pretty much vanished – snuffed out with the advent of street lighting and a surge of coffee houses, and as the amount of time people had available for lying around in bed either sleeping, or in between, shortened.
Actually, you can do your own research and find out that in sleep studies this is now the fairly established view. That is, segmented sleep, bimodal sleep pattern, bifurcated sleep—however it is called—was the normal sleep pattern through most of human existence. References to this divided sleep have been found in the Odyssey. Psalm 119:62 says, “At midnight I will rise to give thanks unto thee because of thy righteous judgments.” Of Paul and Silas in jail it says, “And at midnight Paul and Silas prayed, and sang praises unto God: and the prisoners heard them,” Acts 16:25. And even when Martin Luther writes, “If I fail to spend two hours in prayer each morning, the devil gets the victory through the day,” it is just as likely that he is speaking about the time after midnight between the first and second sleep.
Because that sleep pattern fell out of favor, it means that we can often misinterpret those references when we read them. And, it also means that we can misinterpret the patterns of prayer that developed in the Early Church as a result of those patterns of sleep. The most often misunderstood patterns are the monastic hours of prayer, which the West calls the Canonical Hours. How often have you heard someone commenting on the putative sleep deprivation of the monks and nuns who pray the Midnight Office? For instance, in the Episcopal Café, one article says:
The ancient monastic practice of rising sometime between midnight and two in the morning to pray sanctifies the night hours. To me the idea of nuns and monks rising from their beds in the middle of the night and shuffling down a darkened hall in pairs by candlelight, half asleep, to sing and pray in a cold chapel is both appalling and comforting. … Beyond these memories of sleep deprivation, however, the image of nuns and monks singing in the cold chapel in the middle of the night is comforting. … A friend of mine who is a hermit calls Vigils “the prayer office for pious insomniacs.”
But, that is actually a false assumption. Look closely at the monastic hours. Think in terms of a sleep which begins shortly after dark and is split into two parts. Think in terms of a brief afternoon nap, which is still part of the sleep pattern in many Mediterranean countries. Now, look again at the monastic hours. They fit perfectly into that type of sleep pattern. That is, the monastic hours grew to allow the monks to pray during parts of each of their waking periods, of which the midnight waking period is part.
Thus, contrary to modern popular belief, the Midnight Office was not an office of self-mortification, but a continuation of a pattern as old as the Old Testament, a pattern in which the midnight waking time is a good time to pray. It is a quiet time, a relaxed time during which the soul may most richly pray to God. It is not a time of sleepy prayer, but a time of gentle rich prayer.
I am not suggesting that we all return to that pattern. There is at least one study from France that appears to say that those who have grown up on the modern sleep pattern do not easily switch to the older sleep pattern. This is merely to say that the ancient prayer patterns were not started simply on a whim, but followed the natural cycles of asleep and awake.