The Science of Sleep Apnea: What’s Actually Going On In Your Body

When you think of people with sleep apnea, maybe you picture loud, cartoonish snoring, or assume you’d know something was wrong because you’d wake up feeling completely wiped out every morning. But clinically, sleep apnea is more complex (and easier to miss) than most of us realize.

At its core, “sleep apnea refers to a stoppage of breathing during sleep — reduced or no breathing for 10 seconds or longer,” says Jordan Weiner, MD, a board-certified otolaryngologist and president of Valley ENT in Scottsdale, Arizona. Those pauses can happen dozens of times throughout the night, often without the sleeper having any memory of them.

Sleep apnea affects more people than many realize, with significantly higher rates seen in men. Research suggests that moderate to severe obstructive sleep apnea (OSA) affects roughly two to three times as many men as women, particularly in middle age. Hormones, fat distribution, and differences in airway anatomy all play a role.

Even though these breathing interruptions happen quietly, their effects don’t stay confined to the night. Over time, untreated sleep apnea can ripple through the body, affecting everything from heart health and stress hormones to mood, memory, and focus the next day. Here’s what’s actually going on — physically, emotionally, and cognitively — when sleep apnea flies under the radar.

What Physically Happens During A Sleep Apnea Episode

If you share a bed with a partner, this is usually the part where they chime in. Maybe you’ve been told you snore. Perhaps you’ve been nudged, elbowed, or (gently) kicked in the middle of the night. Snoring happens when airflow is partially blocked and relaxed tissues in the back of the throat vibrate as you breathe — air is still moving, just noisily. But while snoring gets the attention, it doesn’t automatically mean sleep apnea. “Snoring is simply a noise produced by tissues vibrating in the back of the throat,” Weiner explains. “Some people with sleep apnea don’t snore at all.”

So what’s actually happening when someone has true sleep apnea?

After you fall asleep, the muscles in your throat naturally relax. With obstructive sleep apnea, that relaxation becomes a problem. Soft tissues collapse enough to narrow or block the airway, interrupting breathing rather than just causing snoring. “Restricted airflow results in falling oxygen levels in the bloodstream,” says Weiner. When this happens, carbon dioxide levels rise, letting the brain know it's time to start breathing again.

From your body’s perspective, this is an emergency. Specialized sensors in the blood and brain detect the drop in oxygen and rise in carbon dioxide, triggering a surge of adrenaline (epinephrine). Your heart starts beating faster, blood pressure climbs, and your brain steps in to wake the body just enough to restore airflow. (It's a comforting reminder of how our body works smoothly to keep us safe.)

Crucially, most people don’t wake up fully during these episodes. Instead, the brain goes through micro-arousals, which are extremely brief awakenings that last just a few seconds and usually leave no memory the next morning. In more severe cases, people may wake up gasping or feeling panicked, but that’s not the norm. The more common scenario is a brain that’s repeatedly jolted out of deep sleep without ever fully waking.

According to Weiner, just five breathing interruptions per hour is considered abnormal — and many people experience far more. Studies show that those with moderate to severe obstructive sleep apnea experience breathing disruption 15 to 30 or more times an hour, which means this cycle can quietly repeat well over 100 times in a single night. So even though you’re not fully waking up, your body never gets the long, uninterrupted stretches of sleep it needs to properly reset. And that matters, because those deeper stages of sleep are when your brain locks in memories, your emotions recalibrate, and your cells get to do much of their repair work.

How Sleep Apnea Affects Mood And Stress

Sleep apnea does more than interrupt breathing. It repeatedly activates the body’s stress response overnight. Each apnea episode triggers fight-or-flight, sending adrenaline surging and driving up cortisol, the body’s primary stress hormone.

“The body perceives sleep disturbances as stressors,” says Weiner. Over time, that repeated stress response can leave cortisol levels dysregulated. Ironically, people with untreated sleep apnea may wake up feeling exhausted because morning cortisol, which usually helps us feel alert, can be reduced after a night of overproduction.

That stress imbalance doesn’t shut off in the morning. It can follow you into the day as irritability, anxiety, low mood, or a constant feeling of being wired but tired. Studies show people with sleep apnea are significantly more likely to experience mood disorders — proof that even if you’re in bed for eight hours, it’s not just about the amount of time asleep, but the quality of your sleep.

Stress hormones also interact with metabolism. Weiner explains that repeated apnea episodes raise cortisol levels overnight, setting off a chain reaction. “Cortisol raises blood glucose,” he says, prompting the body to release more insulin, which over time “causes increased fat storage in the body and actually reduces the body’s ability to utilize stored fat as a fuel for energy.”

Even with a consistent diet and exercise, appetite signals can become harder to regulate. People with obstructive sleep apnea tend to have higher levels of ghrelin, the hormone that ramps up hunger, and reduced sensitivity to leptin, which helps tell your brain when you’re full. “It’s possible to experience chronic increased hunger if you’re being affected by sleep apnea,” says Weiner. It’s another reason untreated apnea can feel so frustrating and out of sync with healthy habits.

What Sleep Apnea Does to Your Brain

For many people, sleep apnea affects more than sleep itself. It can change how the brain functions during the day. The result is often described as brain fog, difficulty concentrating, forgetting small things, or feeling mentally slower than before.

There’s a real neurological reason for that. “Sleep plays a critical role in memory formation,” says Weiner. New memories are first stored in the hippocampus, then moved during deep sleep to the prefrontal cortex, where they’re meant to live long-term. When sleep keeps getting interrupted, “new memories are not transferred as they should be,” he says. This can result in poorer recall, fuzzy focus, and the sense that your brain just isn’t firing the way it used to.

Research suggests untreated sleep apnea may raise the risk of cognitive decline and dementia. This is likely because the brain is dealing with repeated drops in oxygen and never getting the unbroken sleep it needs to repair and reset.

The Good News: Treatment Can Help

The upside of all this is that sleep apnea is highly treatable, and relief often comes sooner than people expect. “Symptoms usually disappear very quickly,” Weiner says, sometimes within days or weeks once treatment begins. Many people notice deeper, more restorative sleep, better daytime energy, fewer morning headaches, and clearer focus.

Generally, the journey begins with a thorough assessment. Your doctor will review your symptoms, health history, and risk factors, and might suggest a sleep study — either in a clinic or at home — to monitor your breathing, oxygen levels, and sleep patterns overnight. This process helps determine if you have sleep apnea and how severe it is.

Since everyone is unique, chatting with a doctor can really help you find what works best for your body. The goal is to find an approach that keeps the airway open during sleep and reduces the nighttime stress response that keeps jolting the body awake. That may involve strategies that support breathing, improve airway stability, or address contributing factors like sleep position, anatomy, or weight.

Over time, effective treatment does more than help you feel better day to day. It supports your heart, helps steady blood pressure, improves how your body handles energy, and lowers the risk of more serious health issues down the line.

Sleep apnea may happen quietly, but its effects don’t have to stick around. Learning what’s actually going on in your body is often the first, empowering step toward getting the kind of deep, restorative rest you’ve been missing.

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