Sleep Disorders
TL;DR. Roughly a billion people have obstructive sleep apnoea, in which the airway collapses repeatedly during sleep, and the large majority are undiagnosed. Each collapse drops the blood oxygen and jolts the brain briefly awake, hundreds of times a night, which the person does not remember, and the result is exhaustion, high blood pressure, atrial fibrillation, and a several-fold increase in road traffic crash risk. Chronic insomnia affects around 10 percent of adults, and its best treatment is not a tablet: cognitive behavioural therapy for insomnia outperforms sleeping pills and keeps working after it stops. And one sleep disorder, acting out dreams, is the single strongest early warning sign known for Parkinson's disease, often appearing a decade or more before any tremor.
Key takeaways
- Obstructive sleep apnoea affects roughly 1 billion people, and an estimated 80 percent or more of cases are undiagnosed.
- Snoring plus daytime sleepiness plus witnessed pauses in breathing is the combination that should prompt testing, and a partner's account is often more useful than the patient's.
- Treating sleep apnoea lowers blood pressure and dramatically reduces crash risk, though its effect on hard cardiovascular outcomes in trials has been disappointing, largely because people do not use the device enough.
- CBT for insomnia is first-line in every major guideline, and sleeping tablets are a short-term tool with real harms in older adults.
- Restless legs syndrome is frequently caused by iron deficiency, and checking ferritin is standard and often skipped (Chapter 53).
- REM sleep behaviour disorder predicts Parkinson's disease and related conditions in the large majority of people who have it, with a lead time often exceeding a decade.
Obstructive sleep apnoea
In short: The airway repeatedly collapses during sleep, oxygen drops, the brain briefly wakes, and the person remembers none of it.
What actually happens
During sleep, the muscles holding the upper airway open relax. In some people, particularly where the airway is already narrow, it collapses under the negative pressure of inhalation. Airflow stops (apnoea) or is reduced (hypopnoea), oxygen falls, carbon dioxide rises, and the brain produces a brief arousal to restore muscle tone. The person gasps, the airway opens, and sleep resumes.
This can happen 5 times an hour in mild disease and over 30 times an hour in severe disease, all night, every night. The arousals are too brief to be remembered.
The apnoea-hypopnoea index (AHI), events per hour, grades severity: 5 to 15 mild, 15 to 30 moderate, over 30 severe.
Why it damages the body
Each event produces a small physiological emergency, and repeating it hundreds of times a night for years has consequences:
| Mechanism | Consequence |
|---|---|
| Repeated oxygen desaturation and re-oxygenation | Oxidative stress, endothelial dysfunction, systemic inflammation |
| Sympathetic surges with each arousal | Sustained hypertension, including at night when pressure should dip. A leading cause of resistant hypertension (Chapter 20) |
| Large negative pressure swings in the chest | Stretches the atria, promoting atrial fibrillation. Apnoea is one of the strongest reversible risk factors for AF recurrence after ablation |
| Sleep fragmentation | Daytime sleepiness, impaired concentration, mood disturbance, worsened insulin resistance |
Associated outcomes: hypertension, atrial fibrillation, coronary disease, stroke, type 2 diabetes, depression, and a two to seven fold increase in road traffic crash risk, which is why many jurisdictions require declaration to driving authorities.
Who has it
Risk factors: obesity (the dominant one, though a substantial minority of patients are not obese), male sex (though it is substantially under-diagnosed in women, whose symptoms are more often insomnia and fatigue than classic snoring), age, large neck circumference, a set-back or small jaw, large tonsils (the commonest cause in children), nasal obstruction, menopause, alcohol and sedatives before bed, hypothyroidism, and Down syndrome.
Craniofacial structure matters as much as weight in many populations, which is why apnoea is common in East Asian populations at lower BMI than in European ones.
Recognising it
The most useful information usually comes from whoever sleeps next to the patient.
| Symptom | Note |
|---|---|
| Loud snoring with witnessed pauses, then a gasp or snort | The most specific feature |
| Excessive daytime sleepiness | Falling asleep watching television, in meetings, or, dangerously, driving |
| Waking unrefreshed, morning headache, dry mouth | Common |
| Nocturia (waking to urinate repeatedly) | Frequently mistaken for a prostate problem |
| Irritability, poor concentration, low mood | Often the presenting complaint, especially in women |
The STOP-BANG questionnaire (Snoring, Tiredness, Observed apnoeas, Pressure, BMI, Age, Neck circumference, Gender) is a widely used screening tool. Diagnosis is by sleep study, either at home with a portable device or in a laboratory.
Treatment
| Treatment | Detail |
|---|---|
| CPAP (continuous positive airway pressure) | A mask delivering pressurised air that acts as a pneumatic splint holding the airway open. The most effective treatment. Improves sleepiness, blood pressure, and crash risk substantially |
| Mandibular advancement device | A dental appliance holding the lower jaw forward. Less effective than CPAP for severe disease, and better tolerated, so real-world effectiveness can be comparable in mild to moderate disease |
| Weight loss | Directly reduces severity. Tirzepatide was shown in trial to substantially reduce apnoea severity and received a specific approval for it (Chapter 66) |
| Positional therapy | For people whose apnoea occurs mainly on their back |
| Surgery | Tonsillectomy is curative in most children. In adults, upper airway surgery has more variable results. Hypoglossal nerve stimulation, an implant that activates the tongue muscle with each breath, is an option for selected patients who cannot tolerate CPAP |
| Avoiding alcohol and sedatives near bedtime | Both relax airway muscles and worsen events |
The honest note on outcomes. CPAP unquestionably improves sleepiness, quality of life, blood pressure, and driving safety. Randomised trials aiming at hard cardiovascular endpoints, notably SAVE, did not show a reduction in cardiovascular events. The most likely explanation is adherence: average use in those trials was around 3 to 4 hours a night, probably below what is needed, and the trials largely excluded the very sleepy patients who benefit most. So the observational association is strong, the trial evidence for event reduction is weak, and the symptomatic and safety case is clear.
Insomnia
In short: Difficulty sleeping despite adequate opportunity, and the effective treatment is behavioural rather than pharmacological.
What it is. Difficulty falling asleep, staying asleep, or waking too early, despite adequate opportunity, with daytime consequences. Chronic insomnia means at least three nights a week for three months or more, and affects roughly 10 percent of adults, with symptoms in perhaps a third.
How it becomes chronic is best explained by the 3P model:
- Predisposing: a tendency toward hyperarousal, anxiety, or light sleeping.
- Precipitating: a trigger such as stress, illness, bereavement, or shift work.
- Perpetuating: what keeps it going after the trigger has gone. Spending longer in bed to "catch up," napping, clock-watching, and anxiety about sleep itself. These are what treatment targets.
The perpetuating factors are the key insight: the behaviours people adopt to cope with poor sleep are usually the reason it persists.
Treatment.
CBT for insomnia (CBT-I) is first-line in essentially every guideline, outperforms medication in the long term, and its effects persist after treatment ends. Its components:
| Component | What it does |
|---|---|
| Sleep restriction | Deliberately limiting time in bed to roughly the time actually slept, then extending gradually. Counterintuitive, uncomfortable for a week or two, and the most powerful single component |
| Stimulus control | Bed is for sleep and sex only; get up if awake more than about 20 minutes; consistent wake time regardless of the night |
| Cognitive work | Addressing catastrophic beliefs about sleep, which drive the arousal that prevents it |
| Sleep hygiene | The familiar advice. Necessary and, on its own, largely ineffective |
| Relaxation training | Reducing physiological arousal |
Digital CBT-I programmes have good trial evidence and solve the availability problem, since there are nowhere near enough trained therapists.
Medication. Benzodiazepines and Z-drugs (zolpidem, zopiclone) reduce time to sleep by modest amounts, cause tolerance, dependence, and rebound insomnia, impair memory, and increase falls and fractures in older adults. They have a legitimate short-term role in acute crisis. Newer orexin receptor antagonists (suvorexant, lemborexant, daridorexant) block the wake-promoting signal rather than sedating, and appear to have a better profile, though long-term data are limited. Low dose sedating antidepressants and melatonin are also used, melatonin being more useful for circadian timing than for insomnia itself.
Restless legs syndrome
In short: An urge to move the legs, worse at rest and at night, and frequently caused by low iron.
What it is. An uncomfortable, hard-to-describe urge to move the legs, worse at rest, worse in the evening and at night, and relieved temporarily by movement. It affects roughly 5 to 10 percent of adults and can severely disrupt sleep onset. Most patients also have periodic limb movements during sleep, which fragment sleep further.
What causes it. Central dopamine signalling appears to be involved, and brain iron deficiency is central to the current understanding, since iron is a cofactor for dopamine synthesis. Common causes and associations:
- Iron deficiency, and this is the one that must be checked. A ferritin below about 75 µg/L is generally treated even though it would be called normal in other contexts.
- Chronic kidney disease and dialysis.
- Pregnancy, in up to a fifth, usually resolving after delivery.
- Drugs: many antidepressants, antihistamines, and antipsychotics worsen it.
- Family history, which is common.
Treatment: correct iron first. Then, if needed, alpha-2-delta ligands (gabapentin enacarbil, pregabalin) are now generally preferred first-line over dopamine agonists, because dopamine agonists cause augmentation: over months to years the symptoms become more intense, start earlier in the day, and spread to the arms, which is a drug-induced worsening that can be worse than the original condition.
Narcolepsy
In short: Loss of a specific group of brain cells that keep you awake, and it is almost certainly autoimmune.
What it is. Chronic excessive daytime sleepiness with irresistible sleep attacks, affecting roughly 1 in 2,000 people. Type 1 additionally features cataplexy: sudden loss of muscle tone triggered by strong emotion, usually laughter, ranging from a slight jaw drop to complete collapse with full awareness throughout.
What actually goes wrong. Loss of the neurons producing orexin (also called hypocretin), a small hypothalamic population that stabilises wakefulness. Roughly 90 percent of those neurons are gone in type 1 narcolepsy. The evidence that this is autoimmune is strong: an overwhelming association with a specific HLA type (HLA-DQB1*06:02), and a documented increase in cases in some European countries after a particular 2009 H1N1 influenza vaccine and after H1N1 infection itself, which is thought to reflect molecular mimicry in genetically susceptible people.
Other features: sleep paralysis, hypnagogic hallucinations at sleep onset, and disrupted night-time sleep, which surprises people who assume narcolepsy means sleeping well.
Treatment: scheduled naps, plus stimulants or wake-promoting agents (modafinil, solriamfetol, pitolisant) for sleepiness, and sodium oxybate for cataplexy and disrupted night sleep. Diagnosis is frequently delayed by many years, often misattributed to depression or laziness.
REM sleep behaviour disorder
In short: Acting out dreams, and the strongest early warning sign known for Parkinson's disease.
What it is. During REM sleep the body is normally paralysed except for the eyes and diaphragm. In RBD that paralysis fails, and the person physically acts out their dreams: shouting, punching, kicking, leaping from bed. Injuries to the patient and the bed partner are common.
Why it matters far beyond the injuries. Long-term follow-up studies find that the large majority of people with idiopathic RBD go on to develop a synucleinopathy, most often Parkinson's disease or dementia with Lewy bodies, with conversion rates reported above 70 percent at 12 years and higher with longer follow-up. The lead time is frequently a decade or more (Chapter 38).
This makes RBD the most valuable prodromal marker currently available, and it is the population in which trials of disease-modifying Parkinson's treatments are now being designed, because it identifies people before most of the dopamine neurons are lost.
Management: making the bedroom safe (padding, removing sharp objects, sometimes separate beds), melatonin, or clonazepam. And an honest conversation about what it predicts, which patients vary in wanting to have.
Circadian rhythm disorders
In short: The clock is working but set to the wrong time, which is a different problem from insomnia.
| Disorder | Features | Treatment |
|---|---|---|
| Delayed sleep phase | Cannot fall asleep until very late, cannot wake in the morning. Common in adolescents and often mistaken for insomnia or laziness | Timed morning bright light, evening melatonin, gradual schedule shifting |
| Advanced sleep phase | Falling asleep and waking very early. More common with age | Evening bright light |
| Shift work disorder | Sleepiness and insomnia from working against the clock | Strategic light exposure, planned napping, careful shift rotation direction, and, where needed, wake-promoting agents |
| Jet lag | Transient mismatch after travel | Timed light and melatonin; adjust before travelling where possible |
| Non-24-hour rhythm | Common in totally blind people, whose clock has no light input and free-runs | Tasimelteon or melatonin |
Shift work deserves emphasis because it affects around a fifth of the workforce in many countries. Long-term night shift work is associated with cardiovascular disease, type 2 diabetes, obesity, and some cancers, and the International Agency for Research on Cancer classifies shift work involving circadian disruption as probably carcinogenic to humans.
Parasomnias and the rest
In short: Behaviours emerging from the wrong sleep stage, mostly benign, occasionally not.
Sleepwalking, sleep terrors, and confusional arousals arise from incomplete arousal out of deep slow-wave sleep, mostly in the first third of the night, mostly in children, and are usually outgrown. The person has no memory of the event. Triggers include sleep deprivation, fever, alcohol, and some medications. Management is safety (locking doors and windows, removing hazards) rather than drugs. Distinguishing them from RBD matters: parasomnias occur early in the night from deep sleep with no dream recall, RBD occurs later from REM with vivid dream recall.
Sleep paralysis is the opposite failure: REM paralysis persisting into wakefulness, often with frightening hallucinations. It is common, harmless, and frequently terrifying, and simply knowing what it is helps considerably.
Bruxism (tooth grinding) damages teeth and causes jaw pain and headache, and is associated with stress and with sleep apnoea. Treated with a dental splint and by addressing the cause.
Nocturia, waking to urinate, is often attributed to the bladder or prostate when the cause is sleep apnoea, diuretic timing, or fluid redistribution from heart failure.
When to seek help
In short: Four presentations that warrant a sleep assessment rather than a sleeping tablet.
- Snoring with pauses, gasping, or daytime sleepiness, particularly if you have hypertension, atrial fibrillation, or type 2 diabetes.
- Falling asleep while driving, or nearly doing so. This is an emergency, not an inconvenience, and it should stop you driving until assessed.
- Acting out dreams, for the reasons above.
- Insomnia lasting more than three months, which warrants CBT-I rather than an indefinite prescription.
And a general point: unrefreshing sleep despite adequate time in bed is a symptom, not a personality trait. It has a differential diagnosis, and apnoea, restless legs, depression, hypothyroidism, anaemia, and medication effects are all on it.
Sources and notes
Global obstructive sleep apnoea prevalence of approximately 1 billion: Benjafield et al., Lancet Respiratory Medicine, 2019. Undiagnosed proportion: multiple population estimates. Apnoea and crash risk: Tregear et al., Journal of Clinical Sleep Medicine, 2009, meta-analysis. CPAP and cardiovascular outcomes: SAVE trial, McEvoy et al., NEJM, 2016, and subsequent adherence-focused analyses. Tirzepatide for obstructive sleep apnoea: SURMOUNT-OSA, NEJM, 2024. Insomnia prevalence and the 3P model: Spielman et al. CBT-I as first-line: American College of Physicians guideline, 2016, and NICE. Sleeping tablet harms in older adults: Beers criteria and fall/fracture cohort studies. Restless legs and ferritin thresholds: International Restless Legs Syndrome Study Group guidance; augmentation with dopamine agonists: Garcia-Borreguero et al. Narcolepsy orexin neuron loss: Thannickal et al., Neuron, 2000; HLA association and post-H1N1 vaccine cases: Nordic and European pharmacovigilance analyses. RBD conversion to synucleinopathy: Postuma et al., Brain, 2019, multicentre study. Shift work classification: IARC Monographs.
Open questions. Why CPAP has not reduced cardiovascular events in randomised trials despite strong observational associations is unresolved, with adherence the leading explanation. Whether treating RBD, or intervening in that window at all, can delay Parkinson's disease is the central question the field is now designed around.
Next: the conditions of the developing and adult mind that this book has not yet covered. 👉