Two countries, one border
On a map, the line between the United States and Canada looks like someone drew it with a ruler. On the ground, there are long stretches where nothing marks it at all. No river, no fence, just a field where you can stand in one country and take a single step into the other. William Dement opens his chapter on insomnia with that border, because he thinks sleep and wakefulness work the same way: two neighboring countries we cross between twice a day, so often we stop noticing the crossing.
When sleep works, the crossing is routine. When it fails, the border turns into a war zone. Wakefulness refuses to give up its territory at night, and sleep sends raiding parties into the afternoon. Dement describes those borderlands as lawless, a place where you're forced to fend for yourself, and anyone who has stared at a ceiling at 2:40 a.m. knows the description is accurate.
In part two I wrote about my ADHD body clock, which runs about ninety minutes behind the rest of the world. Before I knew there was a name for it, I called it robot mode, a phrase I borrowed from my mentor, Alexander Zahn, who used it for the hours when he was locked in at work. Mine usually switched on after midnight. The night I remember best, I stayed up deep into the night finally doing my expenses, a task I had dodged for weeks, the way ADHD makes you dodge anything boring, unrewarding and due. At 2 a.m. it felt like discipline. The next afternoon it felt like a loan coming due. Chapter six of The Promise of Sleep is Dement's attempt to map the borderlands, and it's the most practical chapter in the book. It's also long enough to need two essays. This one covers what insomnia actually is and what causes it. Part four covers what fixes it.
Is insomnia a disease or a symptom?
In 1977, Dement sat on a panel of psychiatrists, drug researchers and epidemiologists convened by the Institute of Medicine of the National Academy of Sciences to review what science knew about insomnia and sleeping pills. The other panelists were shocked to find almost no good studies on either. Dement and the two other sleep researchers in the room weren't shocked at all. They'd been working in that vacuum for years.
Two decades later, when he sat down to write this chapter, he concluded that the whole field had organized itself around a mistake. Doctors and patients talk about as if it were one illness. Dement's position is blunt. As a single disease, he writes, "there is no such sleep disorder." Insomnia is a symptom, in the same way a stomachache is a symptom. A stomachache can mean appendicitis, gallstones, food poisoning or an ulcer, and each one needs a completely different treatment. Saying "I have insomnia" tells a doctor about as much as saying "my stomach hurts."
He adds a distinction I had never thought about. A sign is something a doctor can observe, like a rash or a fever. A symptom is something only the patient can report. Unless you're sleeping in a lab, no doctor ever watches your insomnia happen, so it lives entirely in your own account of it. That makes you both the witness and the interpreter, and as part four shows, people turn out to be spectacularly unreliable narrators of their own nights.
The modern definition has gotten more precise. Sleep doctors today diagnose chronic insomnia disorder when trouble falling asleep, staying asleep, or waking too early happens at least three nights a week for at least three months, gets in the way of your days, and happens even though you have a real chance to sleep. Roughly a third of adults have some insomnia symptoms, and about one in ten meets the full definition. Dement's core point survives inside the diagnosis: the first job is finding out why.
How many nights of bad sleep is normal?
Dement starts with the cheerful news: a bad night now and then is part of being a person. One summer he woke at 1 a.m. with a mosquito bite. Then came the whine in his ear, the slap, the lamp, the search, the repellent, more whining. By about 2 a.m. he gave up, made coffee, and went to work on the book. He knew he'd pay for it that afternoon, and he also knew exactly why he was awake, so it didn't worry him at all. His long-term fix was to stop leaving the screen door open.
His personal rule goes like this. Wake up in the middle of the night for no reason and fail to get back to sleep, and he'd be annoyed. Same thing the next night, and he'd be concerned. A third night, and he'd start actively hunting for the cause. Specialists call these short runs , and Dement says they make up about three-quarters of all cases. They usually fix themselves when the cause goes away.
The flip side is that a few terrible nights in a row can be dangerous, even when the cause is temporary. Dement tells the story of two sisters, Helen and Rose, vacationing with their families on a California beach the week Iraq invaded Kuwait. Helen's husband, a military reservist, was called to active duty and shipped out to the Persian Gulf within days. Then Rose's husband collapsed on the beach with a blood clot in his lungs and was flown to a hospital by helicopter. Alone with four children and two husbands to worry about, Helen stopped sleeping. When she asked a doctor for help, he refused her a sleeping pill and suggested warm milk.
After four nearly sleepless nights, she packed up the kids to drive about 200 miles to her mother's house. Somewhere in a small town, with relief finally in sight, the debt came due. She drove through a red light without slowing down. She remembers the screech of the pickup's brakes. Miraculously, nobody was killed. The car was totaled.
That's the lesson Dement wants you to keep even if you forget everything else: a temporary cause doesn't make a harmless episode. During the day after several bad nights, he writes, you're like a tightrope walker carrying a heavy load, where one slip or distraction is all it takes.
What causes short-term insomnia?
Dement names three usual suspects. The biggest by far is : stress and worry, which about half of people who've had insomnia name as the cause. How badly it hits depends on how severe the stress is and how long it lasts. Then he adds a detail I love. Happy stress counts too. A lucky windfall, or excitement about something wonderful happening tomorrow, can keep you up just as well as dread. Every kid who ever lay awake on Christmas Eve could have told him that.
The second suspect is time zones and schedule changes: jet lag, shift work, anything that drags your body clock away from your bedtime. The clock keeps sounding its alarm at the old time. Some people catch up in a day or two, and others need a week or more.
The third is the bedroom itself. Noise, light, a snoring partner, the neighbor's bass. Here Dement admits a personal grudge. When he and his wife moved to New York in the late 1950s, their apartment sat right next to an elevated railway, and the screeching brakes of trains pulling into the station kept him up most of the first night. The next morning he was ready to move out. By the following night he was so sleep deprived that he slept straight through the trains, and soon they were just part of the background. People get used to meaningless noise, he says. A noise you suspect someone is making on purpose to annoy you is another story.
His sharpest observation about short-term insomnia is a sad one. When someone is wrecked after a few bad nights, everyone asks the same thing: why don't you just take a nap? The anxiety that keeps them up at night usually keeps them up in the afternoon too. People in the grip of stress tend to fall asleep only when they least want to, at a desk, in a meeting, behind the wheel.
Is it insomnia, or is my body clock just running late?
Once sleep trouble becomes persistent, Dement's first question is simple: is the problem falling asleep, or waking up too early? If it's falling asleep, the culprit is often the clock, specifically that strong evening alerting signal from part one, firing right when you're trying to go to bed. When the whole clock runs so late that you can't fall asleep or wake up at normal times, it's , the condition at the center of my ADHD story in part two.
He showed how often a late clock gets mistaken for insomnia with an experiment from 1970 and 1971, when he was the resident fellow in a Stanford dorm that housed 90 students. He set up a sleep lab in the basement, trained a few very bright students to run it, and recruited volunteers to go to bed at 10 p.m. on various nights. Thirty-six students signed up. Thirty-one of them took more than half an hour to fall asleep, which met the textbook definition of insomnia at the time. Then he had those 31 go to bed at midnight instead.
Thirteen of them fell asleep within ten minutes. None of the students had ever thought of themselves as insomniacs, and Dement doubts any of them had more trouble falling asleep than real patients do. Their problem was a clock telling them that 10 p.m. was still the middle of the evening.
The mirror image is : a clock running early, which knocks you out in front of the TV at 8 p.m. and wakes you at 4 a.m. Waking too early is also a classic sign of depression, which is why Dement always asks early wakers whether they get sleepy in the evening. Light is the treatment in both directions. Bright light in the morning pulls a late clock earlier, and bright light in the evening pushes an early clock later. In 1999 the cutting edge was a pair of glasses that piped light into the edges of your vision through fiber optics, which sounds like something Prince would have worn to the Grammys. Today a light box costs about as much as a pair of decent headphones.
Light timing matters a lot, and getting it wrong can push your clock in the wrong direction. If you think your clock is the problem, a sleep specialist can help you get the timing right.
What does restless legs syndrome feel like?
For people whose persistent insomnia has nothing to do with the clock, Dement says a large share trace back to one of three physical causes. The first sounds like a joke until you hear what it does to people.
is a creepy, crawly, sometimes painful feeling deep in the legs that shows up when you sit or lie still and fades, briefly, when you move. It gets worse in the evening and at night, which is exactly when you're trying to lie still. Dement's two-question test: do you get those feelings when you're sitting or lying down, and do they go away when you walk around? Yes and yes, and the diagnosis is almost certainly RLS.
A Swedish neurologist named Karl Ekbom described the condition in the 1940s, and Dement considers it the second major sleep disorder ever identified, after narcolepsy. He estimated that 15 to 20 million Americans had it, and that most of them had no idea it had a name. At an American Medical Association meeting he asked a room of about 150 physicians how many were familiar with restless legs syndrome. Not one hand went up. In his primary care project in Moscow, Idaho, nearly 30 percent of the patients reported clear symptoms, and not one of them had been diagnosed before.
The stories are brutal. A retired dentist spent more than 15 years unable to sit in a chair long enough to read, assumed it was just part of getting older, and was fixed practically overnight once a doctor recognized it. A veterinarian from San Mateo had it so badly that he'd stand up in the middle of Rotary meetings and pace, then fall asleep the moment he sat back down. He had been thinking about giving up his practice. Treatment, he told Dement, gave him his life back. Dement's files also hold stories of RLS patients who were physically restrained in hospitals for "agitation," which is why he tells anyone who knows they have it to warn every doctor and dentist before a procedure, and to book the aisle seat.
This is the section of the book that has changed the most. RLS now also goes by Willis-Ekbom disease, and studies in North America and Europe put it at roughly 5 to 10 percent of adults, with a smaller group whose symptoms are bad enough to need treatment. In 2024 the American Academy of Sleep Medicine overhauled its treatment guidelines. Checking and correcting iron levels became a central first step, and a class of nerve medications called gabapentinoids moved to the front of the line. The dopamine drugs that dominated treatment for years are no longer recommended for routine use, because over time they can cause , where symptoms get worse, start earlier in the day, and spread to other parts of the body.
That guideline was written for clinicians, and this is my plain-language summary of it, not a treatment plan. Don't start iron supplements without testing first, since too much iron causes its own problems. If the two-question test sounds like you, a doctor can start with a simple blood test.
Can acid reflux, pain or anxiety cause insomnia?
The second physical cause is , stomach acid sliding back up out of the stomach. If it reaches your throat, you wake up coughing or choking. If it only reaches the lower esophagus, you wake up and have no idea why. In lab experiments, a drop or two of acid passed through a tube near the stomach was enough to wake sleepers, even though they didn't report any heartburn. Dement thought reflux was a far more common cause of insomnia than anyone assumed and that almost nobody checked for it. His low-tech advice: don't eat a full meal right before bed.
The third is , a condition of widespread muscle and tendon pain that almost always comes with daytime fatigue and trouble sleeping. Dement was fascinated by a chicken-and-egg question. When healthy volunteers were sleep deprived in experiments, their pain went up. So does the pain disturb sleep, or does broken sleep amplify the pain? Research since has mostly answered: both. Short sleep makes people more sensitive to pain, pain breaks up sleep, and each feeds the other. Treating sleep is now a standard part of treating chronic pain.
Then there's the mind. Persistent sleep trouble shows up alongside depression, anxiety and other psychiatric conditions all the time, and Dement noted that psychiatrists outnumbered sleep specialists by somewhere between 20 and 50 to one. His view was that the insomnia usually clears up once the underlying condition is treated. Modern research has complicated that. Insomnia often arrives before depression and raises the risk of developing it, and it frequently hangs around after mood improves. So doctors today tend to treat the insomnia directly, alongside everything else.
If your sleep trouble comes with low mood, constant worry, or pain, tell your doctor about all of it together. They're often connected.
What can a sleep study show that I can't feel?
When every obvious cause has been ruled out, Dement sends people for an overnight , the full sleep study with wires on your head and legs. Three hidden causes tend to show up there.
The most common is . During sleep the legs flex in a rigid rhythm, usually bending at the big toe, ankle, knee and sometimes hip. The sleeper rarely knows. A bed partner may report getting kicked. What amazed Dement was the regularity: the recording shows bursts of muscle activity at almost exactly 30-second intervals, all night long, like a metronome nobody asked for. It becomes much more common with age, with some studies finding it in up to 40 percent of people over 65.
The second is , where breathing simply stops during sleep and starts again only when the brain wakes up. It's different from the more common obstructive kind, where the airway collapses and the snoring is loud. Dement called central apnea rare and said there was no truly effective treatment for it. Today there are breathing devices designed specifically for it.
The third is the strangest. Some people who complain of severe insomnia show completely normal sleep on the test. Dement called it sleep state misperception. Today it's usually called . A young woman once flew in from the East Coast without an appointment, sat in his office until he showed up, and told him she had quit a Peace Corps assignment overseas because she couldn't sleep. She looked awful. Her daytime nap test showed her less sleepy than the average person. Over two nights in the lab, she fell asleep fairly quickly and slept through the night both times. Both mornings, she was sure she had barely slept at all.
Dement sat down with her and went through the brain-wave recordings page by page. These are beautiful sleep spindles, he told her, this is beautiful deep sleep, and these tests are about as normal as anything he'd seen in his career. He explained that the brain stays busy during sleep, which may be why some people feel like they were awake. He taped the whole conversation and gave her the tape, so that if the worry ever came back, she could listen to it. She flew home and had no further trouble. I would like a copy of that tape. Mine would mostly just say: you slept, man.
Back at the border
What I like most about this chapter is how unglamorous Dement's method is. One night, or many? Trouble falling asleep, or waking too early? Stress, travel, noise, legs, stomach, pain, mood, or a clock that runs late? Every answer points to a different fix, and most of the fixes come in a form other than a pill.
For me, after three parts of this series, the likeliest suspects are the clock from part two and the hyperarousal from this one: a brain that gets quiet and interesting right around 11:40 p.m. The changes I described in part two (leaving Instagram, the gym and sauna before a paper book, the valerian after the shower) were aimed at both. Part four is about what works when trouble sleeping doesn't clear up on its own: the strange behavioral tricks, the long and occasionally deranged history of sleeping pills, and whether my valerian is doing anything at all.
The border isn't going anywhere. The goal is to get through customs a little faster.
Questions people search
What is the main cause of insomnia?
There isn't one. Insomnia is a symptom with many possible causes: stress, schedule changes and jet lag, a noisy or bright bedroom, a body clock that runs late or early, medical conditions such as restless legs, reflux and chronic pain, and mental health conditions like anxiety and depression. Finding the cause is what points to the right treatment.
How many nights of insomnia is normal?
An occasional bad night is common and usually harmless. Chronic insomnia disorder means trouble sleeping at least three nights a week for at least three months, with effects on your daytime life. Several bad nights in a row can still make driving and other risky tasks dangerous.
Can stress cause insomnia even if it's good stress?
Yes. Stress and worry are the most common causes of short-term insomnia, and excitement about something good, like a big event the next day, can keep your brain just as alert.
What's the difference between insomnia and being a night owl?
A night owl's body clock runs late but works fine on a late schedule. When the clock runs so late that you can't fall asleep or wake up at the times your life requires, it may be delayed sleep phase syndrome, which can look exactly like insomnia at a normal bedtime. A sleep specialist can tell them apart.
Why do my legs feel weird when I lie down at night?
A creepy, crawly or aching urge to move your legs that eases when you walk around is the hallmark of restless legs syndrome. It's common, treatable, and sometimes linked to low iron. A doctor can test for it.
Can acid reflux wake you up without heartburn?
Yes. Lab studies found that small amounts of acid in the lower esophagus can wake people who report no heartburn at all. Avoiding a large meal right before bed can help, and a doctor can look into persistent reflux.
Can you think you're awake when you're actually asleep?
Yes. In paradoxical insomnia, also called sleep state misperception, people report severe insomnia while a sleep study shows mostly normal sleep. Many people also underestimate how much they sleep in general.
Is insomnia linked to depression?
Closely, in both directions. Insomnia is common in depression, and research shows ongoing insomnia also raises the risk of developing depression later. It's worth treating directly either way.
Sources
- William C. Dement and Christopher Vaughan, The Promise of Sleep (Delacorte Press, 1999), chapter 6.
- American Academy of Sleep Medicine, International Classification of Sleep Disorders, third edition (chronic insomnia disorder criteria).
- Winkelman et al., "The treatment of restless legs syndrome and periodic limb movement disorder: an American Academy of Sleep Medicine clinical practice guideline," Journal of Clinical Sleep Medicine, 2024.
- Haack et al., "Sleep deficiency and chronic pain: potential underlying mechanisms and clinical implications," Neuropsychopharmacology, 2020.
- Baglioni et al., "Insomnia as a predictor of depression: a meta-analytic evaluation of longitudinal epidemiological studies," Journal of Affective Disorders, 2011.
I'm a guy who reads a lot, not a doctor. Nothing here is medical advice. If sleep is wrecking your days, talk to a physician or a sleep specialist.