Understanding Sleep Apnea

What It Is, Why It Happens, and Why Early Diagnosis Matters

Sleep is meant to be restorative. During healthy sleep, your breathing remains stable, your brain cycles through different stages of sleep, your muscles recover, memories are consolidated, hormones are regulated, and your cardiovascular system gets an opportunity to rest.

Sleep apnea interrupts that process—sometimes hundreds of times every single night.

Many people assume they would know if they had sleep apnea. They imagine loud snoring, gasping for air, or waking up unable to breathe. While those are certainly common signs, sleep apnea is often much quieter than people expect.

In fact, many individuals with clinically significant sleep apnea have no idea it is happening.

What is Sleep Apnea?

According to the latest criteria from the American Academy of Sleep Medicine (AASM), sleep apnea is a sleep-related breathing disorder characterized by repeated reductions or complete pauses in airflow during sleep.

These breathing interruptions disturb normal sleep and place repeated stress on the body throughout the night.

There are three primary types of sleep apnea:

Obstructive Sleep Apnea (OSA)

This is by far the most common form.

Your brain continues sending signals to breathe, but the upper airway narrows or collapses, preventing enough air from reaching the lungs.

Common structures involved include:

the tongue
the soft palate
tissues surrounding the throat
the airway behind the tongue

As airflow becomes restricted, the body works harder and harder to breathe until the airway eventually reopens.

Central Sleep Apnea (CSA)

Central sleep apnea is different.

Rather than the airway collapsing, the brain temporarily fails to send an appropriate breathing signal to the respiratory muscles.

There is little or no breathing effort during these events.

Central sleep apnea is less common and is often associated with neurological conditions, heart failure, opioid medications, or certain medical treatments.

Complex Sleep Apnea Syndrome

Also called Treatment-Emergent Central Sleep Apnea, this occurs when obstructive sleep apnea is treated (usually with CPAP), but central apneas emerge or persist.

A sleep physician determines whether this diagnosis applies.

What Actually Makes Us Breathe?

One of the biggest misconceptions in medicine is that oxygen is what makes us breathe.

It seems intuitive—after all, we breathe in oxygen. Surprisingly, however, our primary drive to breathe comes from carbon dioxide (CO₂), not oxygen.

Every second your body's cells produce carbon dioxide as a natural waste product of metabolism. As CO₂ enters the bloodstream, it combines with water in the plasma through the action of the enzyme carbonic anhydrase.

The reaction is:

CO₂ + H₂O ⇌ H₂CO₃ ⇌ HCO₃⁻ + H⁺

The bicarbonate (HCO₃⁻) helps buffer the blood, but it is the hydrogen ions (H⁺) that are especially important. As hydrogen ion concentration increases, the blood becomes more acidic and the pH decreases.

Your body continuously monitors these subtle changes.

Specialized chemoreceptors within and around the brainstem—along with the blood-brain barrier's regulation of carbon dioxide and pH—detect when acidity begins to rise. Peripheral chemoreceptors in the carotid and aortic bodies also contribute, particularly when oxygen levels become significantly reduced.

When these sensors detect rising CO₂ and falling pH, they send an urgent signal:

"Breathe harder. Breathe deeper. Breathe now."

This remarkably sensitive system works continuously throughout the day and night without us ever thinking about it.

What Happens if This Continues for Years?

The human body is incredibly adaptable.

When exposed to repeated nightly breathing disturbances over months or years, the body can undergo changes in how breathing is regulated, how the cardiovascular system responds to stress, and how the autonomic nervous system functions.

Researchers continue to study how chronic intermittent hypoxia and repeated elevations in carbon dioxide influence ventilatory control and chemoreceptor sensitivity. In some individuals, these adaptations may contribute to more unstable breathing patterns during sleep or complicate the management of sleep-disordered breathing. However, the progression from obstructive sleep apnea to central sleep apnea is complex and depends on multiple factors, including underlying heart, neurological, or respiratory conditions.

The important takeaway is this:

Sleep apnea is not simply about snoring or oxygen levels.

Every untreated breathing event forces your body to repeatedly choose survival over restoration. Night after night, the brain is asked to correct an airway problem instead of allowing the body to recover, repair tissues, consolidate memories, regulate hormones, and maintain cardiovascular health.

This is one of the reasons healthcare professionals encourage early diagnosis and treatment—not simply to improve sleep quality, but to reduce the long-term physiological stress that untreated sleep-disordered breathing can place on the body.

Learn more about The Sympathetic Nervous System: Why Your Body Thinks It's Being Choked Every Night.

How Severe is Sleep Apnea?

Sleep apnea is commonly classified using the Apnea-Hypopnea Index (AHI), which represents the average number of breathing interruptions per hour of sleep.

General adult classifications include:

Severity	AHI
Normal	Less than 5 events/hour
Mild	5–14.9 events/hour
Moderate	15–29.9 events/hour
Severe	30 or more events/hour

While these categories are useful, they do not tell the entire story.

Someone with "mild" sleep apnea may experience significant symptoms because of frequent sleep fragmentation, oxygen fluctuations, or repeated arousals. Conversely, another individual with a higher AHI may report surprisingly few symptoms.

Severity is only one piece of the puzzle. Oxygen levels, sleep fragmentation, cardiovascular responses, symptoms, and medical history are equally important.

Can You Have Sleep Apnea Without Snoring?

Absolutely.

Although snoring is often considered the classic sign of obstructive sleep apnea, it is not required for the diagnosis.

Throughout our years working with thousands of sleep studies, we have encountered numerous patients with clinically significant sleep apnea who barely snore—or do not snore at all.

Snoring occurs when soft tissues vibrate as air struggles to pass through a narrowed airway.

Common structures responsible include:

the soft palate
the tongue
tissues at the back of the throat

(Learn more about the anatomy of the soft palate.)

However, some people experience repeated airway collapse/ restriction without producing significant snoring.

Others may primarily experience subtle breathing resistance rather than complete airway obstruction.

Can Snoring Alone Disrupt Your Sleep?

Yes.

Many people believe that snoring is simply a nuisance for their partner.

In reality, snoring itself can fragment sleep.

When the airway becomes partially restricted, your body must generate greater breathing effort to maintain airflow.

Sometimes this increased effort causes the brain to briefly wake just enough to restore normal breathing—even though no complete apnea has occurred.

These events are called Respiratory Effort-Related Arousals (RERAs).

They often occur in individuals with:

Upper Airway Resistance Syndrome (UARS)
early obstructive sleep apnea
patients whose breathing disturbances do not yet meet traditional sleep apnea thresholds

Repeated arousals prevent the brain from maintaining stable sleep, leaving people feeling exhausted despite spending adequate hours in bed.

Interestingly, this pattern is frequently observed in women.

Research has shown that many women have a lower threshold for waking in response to increased breathing effort. Instead of sleeping through severe oxygen drops, they often experience repeated sympathetic nervous system activations that fragment sleep long before oxygen levels become dramatically abnormal.

For patients suspected of having milder sleep-disordered breathing, respiratory effort-related arousals become especially important.

This is one reason devices such as the WatchPAT ONE can provide valuable information, as they are capable of detecting physiological changes associated with respiratory effort that traditional home sleep tests may miss.

(Learn more about our WatchPAT ONE Home Sleep Test.)

What Happens During an Apnea?

An apnea is far more than "holding your breath."

According to current AASM scoring criteria, an obstructive apnea occurs when airflow decreases by at least 90% from baseline for at least 10 seconds while breathing effort continues WITH an oxgen desaturation of 3% or greater.

Your airway closes.

Your diaphragm continues trying to pull air into the lungs.

Your chest continues working.

But very little—or no—air enters.

As oxygen levels begin to fall and carbon dioxide rises, your body recognizes something is wrong.

Within seconds, one of the body's oldest survival systems activates.

Your sympathetic nervous system—the "fight-or-flight" response—takes over.

This results in the release of stress hormones including:

adrenaline (epinephrine)
noradrenaline
cortisol

Blood pressure rises.

Heart rate increases.

Blood glucose is mobilized to prepare your body for immediate action.

Your brain briefly arouses from sleep just enough to reopen the airway.

Most people never remember these awakenings.

But physiologically, they absolutely occur.

Every apnea is essentially a miniature emergency response occurring while you are supposed to be recovering.

This repeated activation not only fragments sleep but places continuous physiological stress on nearly every organ system.

Just because you remain asleep does not mean your body is unaware.

A useful analogy is childhood development.

A baby may not consciously remember every experience, but the sights, sounds, and stressors surrounding them still influence development.

Likewise, your sleeping brain and body continue responding to every interruption in breathing—even if you have no conscious memory of it the next morning.

Repeated sympathetic activation also contributes to frequent nighttime awakenings and is one reason many people begin developing nocturia, the need to wake repeatedly during the night to urinate.

(Learn more about sleep architecture.)

(Learn more about nocturia.)

Why Does REM Sleep Matter?

Rapid Eye Movement (REM) sleep is one of the most fascinating—and important—stages of sleep.

It is during REM sleep that:

dreaming is most vivid
memory consolidation occurs
emotional processing takes place
the brain performs important restorative functions
grey matter health is supported

Ironically, REM sleep is also when obstructive sleep apnea often becomes the worst.

During REM, nearly every skeletal muscle in the body temporarily loses tone.

This protective mechanism prevents us from physically acting out our dreams.

Unfortunately, it also makes the upper airway significantly more likely to collapse.

Your tongue relaxes.

The muscles supporting your airway relax.

The soft palate becomes more prone to obstruction.

Meanwhile, your eyes move rapidly beneath closed eyelids and small, fast muscle twitches occur throughout the body.

This combination creates the perfect environment for obstructive sleep apnea.

Many patients demonstrate relatively stable breathing during lighter stages of sleep, only to experience clusters of breathing events every 60 to 90 minutes as they enter REM sleep.

This pattern is something we frequently observe during sleep testing.

The question then becomes:

If your breathing repeatedly collapses during the very stage of sleep responsible for restoration, memory, learning, emotional regulation, and recovery…

...how restorative is your sleep actually becoming?

Understanding Sleep Apnea is the First Step

Sleep apnea is far more than snoring.

It is a complex physiological disorder that repeatedly interrupts sleep, activates stress responses, affects oxygen delivery, alters cardiovascular function, and prevents the brain from obtaining the restorative sleep it requires.

Fortunately, it is also one of the most treatable sleep disorders.

If you experience symptoms such as excessive daytime fatigue, witnessed pauses in breathing, loud snoring, morning headaches, frequent nighttime awakenings, unexplained high blood pressure, or persistent daytime brain fog, discussing these symptoms with your physician is worthwhile.

Early diagnosis allows treatment before years of repeated physiological stress accumulate.

Because better sleep is not simply about sleeping longer.

It is about allowing your body the uninterrupted opportunity to recover, repair, and prepare for tomorrow.