If you stop breathing during sleep, the most likely explanation is sleep apnea, a condition where your airway either physically collapses or your brain temporarily fails to send breathing signals to your muscles. It affects an estimated 936 million adults worldwide between the ages of 30 and 69, and up to 80% of people with moderate-to-severe cases have no idea they have it. Understanding why it happens is the first step toward fixing it.
How Your Airway Closes During Sleep
The most common form, obstructive sleep apnea, is a mechanical problem. When you’re awake, muscles in your throat keep the airway open. When you fall asleep, those muscles relax. For most people, this relaxation is harmless. But if your airway is already narrow, even a modest loss of muscle tone can cause it to partially or fully collapse.
The key player is a muscle called the genioglossus, which acts as the main dilator keeping your upper airway open. During sleep, the reflexes that activate this muscle weaken, and the tongue can slide backward into the throat. Several anatomical features make this worse: an enlarged tongue, oversized tonsils, a long or drooping soft palate, an elongated uvula, or redundant folds of tissue in the pharynx. A smaller jaw or narrow facial skeleton also increases the external pressure on the airway, making collapse more likely.
Excess weight compounds the problem. Fat deposits in the tongue and surrounding throat tissues physically shrink the airway’s diameter. This is why neck circumference is a useful screening marker. A neck larger than 17 inches in men or 16 inches in women signals higher risk, because it typically reflects excess fat in the area surrounding the airway.
When the Brain Forgets to Breathe
Central sleep apnea is less common but works completely differently. Your airway stays open, but your brain temporarily stops sending signals to the muscles that control breathing. The problem originates in the brainstem, where specialized neurons generate your breathing rhythm based on feedback from sensors that monitor carbon dioxide and oxygen levels in your blood.
When these brainstem pathways are damaged or disrupted, the feedback loop breaks down. In some cases, the brain becomes overly sensitive to carbon dioxide, overcorrecting with deep breaths and then pausing when CO2 drops too low. This creates a distinctive pattern of breathing that waxes and wanes: cycles of increasingly deep breaths followed by increasingly shallow ones, then a complete pause. This pattern is closely associated with heart failure and with damage to nerve fibers connecting the frontal brain regions to the brainstem respiratory centers.
Signs You Might Not Recognize
Loud snoring is the symptom most people associate with sleep apnea, but it’s far from the only one. Many people notice they wake up gasping or choking, sometimes multiple times per night. Bed partners often witness the pauses in breathing directly.
Other symptoms are easier to miss. Morning headaches, frequent nighttime urination, acid reflux that worsens at night, difficulty staying asleep, and persistent daytime sleepiness even after a full night in bed all point toward disrupted breathing during sleep. Cognitive effects like trouble concentrating, memory problems, and brain fog are common too, especially in mild cases where sleepiness alone might not seem severe enough to investigate.
Who Is Most at Risk
Roughly 26% of Americans between 30 and 70 have at least mild obstructive sleep apnea, and about 10% have moderate-to-severe disease. Men are affected at higher rates than women, though the gap narrows significantly after menopause. Prevalence in European populations runs between 6% and 17%, while studies in urban Chinese populations have found rates as high as 27%.
Beyond weight and neck size, your risk increases with age, a family history of sleep apnea, nasal congestion, alcohol use before bed (which further relaxes throat muscles), and sleeping on your back. Smoking, which causes inflammation and fluid retention in the upper airway, is another contributing factor.
What Untreated Sleep Apnea Does to Your Body
Each time your breathing stops, oxygen levels in your blood drop. These repeated dips, sometimes dozens or hundreds of times per night, trigger a cascade of problems. Your body releases surges of adrenaline-like hormones through the sympathetic nervous system, spiking your blood pressure and heart rate even while you’re supposed to be resting. Over time, this leads to persistent high blood pressure that’s often resistant to medication.
The damage goes deeper than blood pressure. The repeated oxygen drops activate inflammatory pathways throughout the body, damaging blood vessel walls and accelerating the buildup of arterial plaques. This process begins before full-blown atherosclerosis develops, with blood vessels losing their ability to dilate properly. The heart itself suffers too: the muscle walls thicken, the chambers enlarge, scar tissue forms between heart fibers, and the heart’s pumping efficiency drops. Sleep apnea is independently linked to heart attack, heart failure, and stroke.
How Sleep Apnea Is Measured
Diagnosis hinges on counting how many times per hour your breathing stops or becomes dangerously shallow during sleep. This number, called the apnea-hypopnea index (AHI), defines severity: 5 to 14 events per hour is mild, 15 to 30 is moderate, and above 30 is severe.
The gold standard test is an overnight study in a sleep lab, where sensors track your breathing, oxygen levels, brain waves, and body position. Home sleep tests are now widely available and more convenient. They’re reasonably accurate for detecting moderate-to-severe cases, with about 80% sensitivity and 83% specificity compared to in-lab testing. They’re less reliable for milder cases or for central sleep apnea, so a normal home test doesn’t always rule the condition out.
Treatment That Makes a Measurable Difference
Continuous positive airway pressure (CPAP) remains the most effective treatment. A CPAP machine delivers a steady stream of air through a mask, acting as a pneumatic splint that keeps the airway from collapsing. The health benefits are substantial. A study of Medicare-eligible adults found that people who started CPAP had roughly half the risk of dying over the following five years compared to those who didn’t. For people with no prior heart disease, starting CPAP was associated with a 10% lower risk of a major cardiovascular event, with the strongest protection against heart attack specifically, at a 16% risk reduction.
CPAP isn’t the only option. Oral appliances that reposition the lower jaw forward can work well for mild to moderate cases. Weight loss, when applicable, directly reduces the tissue bulk compressing the airway. For people whose apnea is significantly worse when sleeping on their back, positional therapy can be surprisingly effective. In mild and moderate positional cases, simply keeping off your back has been shown to reduce breathing interruptions as effectively as CPAP. The simplest version involves attaching something bulky to the back of your sleepwear, though newer vibrating devices worn on the chest detect when you roll onto your back and gently prompt you to shift position. The older tennis ball technique, while intuitive, has poor long-term adherence because it’s uncomfortable enough that most people eventually abandon it.
Surgical options exist for people with clear anatomical obstructions, such as enlarged tonsils or a severely recessed jaw, that can’t be managed with other approaches. The right treatment depends heavily on what’s causing your specific pattern of airway obstruction and how severe it is.