Being well-rested is elusive these days: wireless internet access blurs the line between work and personal time, and the ‘cult of busy’ blossoms. Within the spare hours during which we do permit ourselves to sleep, the glow of electronics and the Ghost of Work Future can delay and disrupt our rest. Sleepers everywhere commonly report trouble falling asleep, waking up alert in the middle of the night, or feeling tired throughout the day. Certainly, stress and visual stimuli are plausible culprits of difficulties falling asleep and thus of daytime fatigue, and dietary habits appear guilty too, as more and more people credit cutting added sugar with newfound energy. Midnight alertness, though, doesn’t add up, at least in my personal experience.
“For many, though, these waking episodes are accompanied by anxiety about their apparent trouble sleeping, which compounds daytime tiredness.”
As a graduate student in science, I’m a part of the demographic that allegedly consumes more coffee than any other working folks do. A cup of coffee switches out my to-do list for serial looming emergencies, though, so to stay awake and effective at work, I actually sleep at night—a lot. I’m one of those delicate flowers (namely, a pansy) who needs nine hours to function, and I’m a night owl, too. So I’ve always been perplexed that when I do occasionally wake up around 3 in the morning, I feel sharply alert, deeply calm, and ready to face the day that hasn’t begun. The feeling lasts about two hours before I feel ready to go back to sleep. Over time, I’ve begun to tackle lab-related or creative work during these hours, which seem optimized for just that. For many, though, these waking episodes are accompanied by anxiety about their apparent trouble sleeping, which compounds daytime tiredness.
Surprisingly, a little historical digging reveals that this waking period is so common because it isn’t a problem at all – rather, it’s a hallmark of how people slept until recently. Until the widespread use of gas lamps and electric lighting, our schedules were powerfully governed by daylight. There wasn’t much labor to be done or family time to enjoy by candlelight or in darkness, so many people went to bed after sunset, slept for three to four hours, and then awoke naturally. The next three to four hours were often spent on prayer, reflecting on dreams, having sex, socializing with neighbors, or even petty crime. People then returned to sleep until dawn.
This pattern of two sleep shifts over twelve hours is currently called “segmented sleep” or “biphasic sleep.” The phenomenon is less surprising in itself than the fact that it disappeared from collective memory so quickly: in grand historical terms, its fade from the mid-17th to 19th centuries is quite recent. The transition to a single block of sleep, and to sleeping fewer total hours, was stimulated by twenty-four hour lighting and propelled by the heavier work demands of the Industrial Revolution.
However, proof of segmented sleep has been thoroughly chronicled by historian Robert Ekirch, who has curated hundreds of references to “first sleep” and “second sleep” in several languages in diaries, medical records, and so on. His acclaimed book At Day’s Close: Night in Times Past includes a suggestion from a French medical pamphlet that the best time for young couples to conceive a child was when they were partially rested between first and second sleeps, and even a possible reference to the phenomenon from Homer’s Odyssey:
“Two gates the silent house of Sleep adorn;
Of polish’d ivory this, that of transparent horn:
True visions thro’ transparent horn arise;
Thro’ polish’d ivory pass deluding lies.”
Segmented sleep is a function of biology, not only of preindustrial culture. Most animals sleep in two or more chunks per day. Ekirch has also found that segmented sleep is practiced in modern tribal cultures. In 1992, researcher Thomas Weir placed eight men in darkened rooms for fourteen hours per day during the evening and night for one month, and asked them to restrict their sleep to that dark period. By the end of the month, the men had settled into the same segmented sleep pattern found elsewhere: three to four hours of sleep beginning at “dusk,” three to four hours of wakefulness, and then three to four more hours of sleep.
These days, people who wake during the night tend to become anxious about it, thereby compounding the issue, but doctors familiar with segmented sleep are beginning to assure patients and the general public that what appears to be insomnia is completely physiologically normal. In fact, segmented sleep promotes healthy endocrine function in a way that a single block of sleep cannot. Segmented sleepers release a surge of a hormone called prolactin before waking during the night, which sets off a cascade of sex hormones. The cascade ends in the release of the hormone progesterone, which triggers the sleepiness and the start of the night’s second sleep.
“doctors familiar with segmented sleep are beginning to assure...the general public that what appears to be insomnia is completely physiologically normal”
For people who sleep in a single block through the night, this prolactin surge is much smaller, and the body responds by releasing small amounts of prolactin throughout the day, which is harmful and leads to a condition called hyperprolactinemia. General sexual dysfunction, a loss of menstruation in women, and an enlarged pituitary that ultimately causes headaches or vision problems may result; later in life, sufferers may even develop osteoporosis. Obviously, this isn’t the case for everyone who sleeps through the night, but it serves as an earnest to change behavior.
Of course, it may not be practical for many people to seek out dusk-to-dawn segmented sleep practices; most of us don’t have enough time away from work to sleep for eight hours even without a break between four-hour shifts. At least, though, it is important to understand that midnight wakefulness isn’t something to worry about, and it can even be the most peaceful or productive time of the day, if we allow it to be.
