Polysomnography: What to Expect During a Sleep Study and How Results Are Interpreted

When you’re tired all the time, even after a full night’s sleep, something deeper might be going on. Snoring loudly, waking up gasping, or feeling exhausted despite sleeping eight hours? These aren’t just annoyances-they could be signs of a sleep disorder. That’s where polysomnography comes in. It’s not just another test. It’s the most detailed way doctors can see what’s really happening while you sleep.

What Exactly Is a Polysomnography?

Polysomnography, or PSG, is a sleep study that records your body’s activity while you sleep. The word itself breaks down into three parts: poly (many), somno (sleep), and graphy (recording). So it’s a multi-parameter sleep recording. Unlike a quick home test that only checks breathing, a polysomnography watches your brain, eyes, heart, muscles, breathing, and oxygen levels-all at once.

This isn’t just about spotting sleep apnea. It can catch narcolepsy, restless legs syndrome, night terrors, sleepwalking, and even seizures that happen while you’re asleep. The American Academy of Sleep Medicine says it’s the gold standard because it tracks sleep stages-something simpler tests can’t do. You can’t diagnose narcolepsy without seeing if you’re entering REM sleep too fast. You can’t tell the difference between obstructive and central sleep apnea without watching chest and abdominal movement. That’s why PSG is still the go-to test, even with newer home options available.

What Happens During the Test?

You show up at a sleep center about an hour before your usual bedtime. The room looks like a hotel room-quiet, dark, with a comfortable bed. No machines hanging from the ceiling. Just a few wires and sensors.

A sleep technologist attaches around 22 sensors to your body. These aren’t needles. They’re sticky patches and soft bands. One on your scalp to read brain waves (EEG). Two near your eyes to track movement (EOG). A small sensor on your chin and legs to measure muscle activity (EMG). Belts around your chest and belly to detect breathing effort. A tiny tube under your nose to measure airflow. A clip on your finger to check blood oxygen (pulse oximetry). And a camera in the corner to record any unusual movements or sounds.

You might feel weird at first. Like you’re wearing a weird hat with wires. Some people can’t fall asleep the first night-this is normal. About 85% of patients get enough sleep for a valid result. The technologist is watching you from another room, ready to help if a sensor comes loose or you need to use the bathroom. You can talk to them anytime.

The whole test lasts 6 to 8 hours. You’re not locked in. You can get up if you need to. The room is kept between 68 and 72 degrees Fahrenheit so you’re not too hot or cold. No caffeine after noon the day before. No naps. Just try to sleep like you normally would.

How Is the Data Analyzed?

After the test, you go home. The real work starts for the sleep doctor.

The machine records over 1,000 pages of raw data. That’s not an exaggeration. Every second of your sleep is broken down into 30-second chunks. Each chunk gets scored: Were you in light sleep? Deep sleep? REM? Did you have a breathing pause? Did your oxygen drop? Did your leg jerk? Did your heart skip?

Sleep specialists look for patterns. For example:

• If you stop breathing 15 times an hour, that’s moderate sleep apnea.
• If your oxygen drops below 90% during those pauses, that’s a red flag.
• If you enter REM sleep within 15 minutes of falling asleep, that’s a sign of narcolepsy.
• If your legs kick every 20 seconds, that’s restless legs syndrome.
• If you scream or punch the air during sleep, it could be REM sleep behavior disorder.

The report doesn’t just say “you have sleep apnea.” It gives numbers: apnea-hypopnea index (AHI), oxygen nadir, sleep efficiency, time in each stage. That’s how doctors decide if you need CPAP, oral appliances, or just lifestyle changes.

Polysomnography vs. Home Sleep Tests

Home sleep tests are cheaper and more convenient. But they’re limited. Most only measure breathing, airflow, oxygen, and heart rate. That’s it. They can’t tell if you’re sleeping at all. They can’t catch narcolepsy. They can’t diagnose parasomnias. And they fail 15-20% of the time because sensors fall off or you don’t wear them right.

In-lab polysomnography fails less than 5% of the time. It’s more accurate. It’s more complete. Insurance companies know this. Medicare and most private insurers will only cover a home test if you have a high likelihood of moderate-to-severe obstructive sleep apnea and no other sleep disorders. If you have high blood pressure, heart disease, or neurological symptoms? You’ll likely need a full PSG.

There’s also split-night PSG. If you have severe apnea in the first half of the night, the technician might wake you up and fit you with a CPAP mask. Then they’ll adjust the pressure while you sleep the rest of the night. That means you don’t need to come back for a second test.

What Do the Results Mean?

Your doctor will sit down with you and explain the numbers. Here’s what common results mean:

• AHI 5-15: Mild sleep apnea. Might need weight loss, positional therapy, or a mouthpiece.
• AHI 15-30: Moderate. CPAP is usually recommended.
• AHI over 30: Severe. CPAP is almost always needed.
• Oxygen below 90%: Your body isn’t getting enough air. This raises your risk for heart problems.
• Low sleep efficiency (under 85%): You’re not sleeping well even if you’re in bed long enough.
• Short REM latency (under 15 minutes): Could mean narcolepsy or other neurological sleep disorders.

If the test shows no breathing issues but you’re still exhausted? That’s when other disorders come into play. Restless legs? Periodic limb movements? Parasomnias? PSG catches them all.

What If the Test Is Normal?

Sometimes, the results come back normal. You’re not apneic. Your oxygen is fine. Your sleep stages look normal. But you’re still tired.

That doesn’t mean it’s all in your head. It means the cause might be outside the scope of PSG. Maybe you have circadian rhythm disorder. Maybe your thyroid is off. Maybe you’re not getting enough deep sleep because of stress or anxiety. Your doctor might recommend a second test-like a Multiple Sleep Latency Test (MSLT)-to check for narcolepsy. Or they might look at your mental health, diet, or medication side effects.

Don’t dismiss a normal PSG. It’s still valuable. It rules out major sleep disorders so you can focus on other causes.

What’s New in Sleep Studies?

Technology is changing. New wireless sensors mean fewer wires. Instead of 20 cables, you might have just five. Some labs use AI to help score data faster and more accurately. Cloud-based systems let specialists review results from anywhere.

But the core hasn’t changed. You still need to sleep in a lab with sensors on your head. Why? Because nothing else can capture the full picture of your sleep. Home tests are growing, but they’re not replacements. They’re shortcuts-for simple cases only.

The American Academy of Sleep Medicine says polysomnography will remain the standard through at least 2030. Why? Because sleep isn’t just about breathing. It’s about brain waves, muscle control, heart rhythm, oxygen flow, and behavior-all happening at once. Only PSG sees it all.

How to Prepare for Your Sleep Study

You don’t need to do much-but do these things:

• Avoid caffeine after noon the day before.
• Don’t nap during the day.
• Wash your hair-no gels or oils. Sensors need clean skin.
• Bring comfortable pajamas, your own pillow if you like, and anything you need for a good night’s sleep.
• Write down your symptoms: When do you snore? Do you wake up choking? Do you feel sleepy during the day?
• Bring a list of all your medications. Some affect sleep.

Most people are surprised by how easy it is. The sensors don’t hurt. The room is quiet. The staff is helpful. You’re not alone. About 90% of patients who get proper instructions say they’d do it again.

Insurance and Cost

In the U.S., Medicare covers 80% of the cost if your doctor documents symptoms like loud snoring, witnessed apneas, or excessive daytime sleepiness. Private insurers usually require prior authorization. The test can cost $500 to $3,000 without insurance. Home tests are $150 to $500-but again, they’re not always enough.

If your doctor says you need a PSG, don’t delay. Untreated sleep apnea raises your risk for stroke, heart attack, and diabetes. Poor sleep affects your mood, memory, and even your job performance. Getting this test done could change your health for years to come.