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

When you’re tossing and turning every night, waking up exhausted even after eight hours in bed, it’s not just bad sleep-it might be something deeper. That’s where polysomnography comes in. It’s not a simple snore monitor or a wearable tracker you buy online. It’s the gold standard sleep study used by doctors to find out exactly what’s going wrong while you sleep. And if you’ve been told you need one, you’re probably wondering: What’s it really like? What do they measure? And what do the results actually mean?

What Exactly Is a Polysomnography?

Polysomnography, often called PSG or a sleep study, is a full-night test that records your body’s activity while you sleep. The name breaks down simply: poly means many, somno means sleep, and graphy means recording. So, it’s a multi-parameter sleep recording. Unlike home sleep tests that only check breathing, polysomnography looks at your brain, eyes, muscles, heart, breathing, oxygen levels, and even how you move-all at once.

It’s done in a sleep center, usually a quiet, private room that looks like a hotel room but with wires and sensors everywhere. You’ll arrive a couple of hours before your normal bedtime so technicians can set everything up. They’ll attach about 20 sensors to your scalp, face, chest, legs, and fingers. It sounds intense, but it’s painless. No needles. No shocks. Just sticky pads and soft belts.

The whole test lasts 6 to 8 hours-enough time to go through several full sleep cycles. A sleep technologist watches you from another room on monitors, making sure the data is clean and stepping in if you need help adjusting a sensor or just want to talk.

What Does a Polysomnography Measure?

This isn’t just one thing being tracked. It’s a full-body snapshot of your sleep. Here’s what’s actually being recorded:

• Brain waves (EEG): Electrodes on your scalp pick up electrical activity to tell which sleep stage you’re in-light sleep, deep sleep, or REM. This is critical because disorders like narcolepsy mess with how you enter REM sleep.
• Eye movements (EOG): These help detect REM sleep, when your eyes dart around under closed lids. If you’re having nightmares or acting out dreams, this helps spot it.
• Muscle activity (EMG): Sensors on your chin and legs track muscle tone. Twitches, leg jerks, or even sleepwalking show up here.
• Heart rhythm (ECG): Your heart doesn’t stop during sleep. This records irregular beats or drops in heart rate that could signal other health issues.
• Respiratory effort: Two elastic belts around your chest and belly measure how hard you’re trying to breathe. This helps tell the difference between obstructive sleep apnea (blocked airway) and central sleep apnea (brain didn’t signal to breathe).
• Airflow: A tiny tube under your nose or a pressure sensor detects whether air is moving in and out. No airflow? That’s an apnea.
• Blood oxygen (SpO2): A clip on your finger tracks how much oxygen your blood is carrying. If it drops below 90%, that’s a red flag.
• Body position: Are you sleeping on your back? Side? This matters because sleep apnea often gets worse when you’re on your back.
• Audio and video: The room is quietly recorded so technicians can hear snoring, gasping, or even talking and kicking in your sleep.

All this data gets combined to build a full picture of your sleep architecture-the natural rhythm between light, deep, and REM sleep. Normal sleep cycles last about 90 minutes and repeat 4 to 6 times a night. If you’re skipping stages, waking up too often, or jumping into REM too fast, something’s off.

Who Needs a Polysomnography?

Not everyone who snores needs this test. But if you have symptoms like:

• Chronic loud snoring with pauses in breathing (witnessed by a partner)
• Daytime exhaustion that doesn’t improve with more sleep
• Waking up gasping or choking
• Unexplained morning headaches
• Frequent nighttime urination
• Restless legs that wake you up
• Acting out dreams-kicking, yelling, punching
• Unexplained sleepwalking or night terrors

…then your doctor might recommend a polysomnography. It’s the only test that can diagnose:

• Obstructive sleep apnea (OSA)
• Central sleep apnea (CSA)
• Narcolepsy
• Idiopathic hypersomnia
• Parasomnias (sleepwalking, night terrors, REM sleep behavior disorder)
• Periodic limb movement disorder
• Unexplained insomnia with suspected underlying causes

Home sleep tests are cheaper and easier, but they only check breathing and oxygen. They miss everything else. If you have narcolepsy, your brain doesn’t follow normal sleep patterns-but a home test won’t catch that. If you’re kicking your legs every 30 seconds, a home test won’t know. That’s why specialists still rely on polysomnography for anything beyond simple, clear-cut sleep apnea.

What’s a Split-Night Study?

Sometimes, the answer comes fast. If you’re having severe sleep apnea in the first half of the night, the technician might switch you to a split-night study. That means after diagnosing the problem, they’ll wake you up and fit you with a CPAP mask. Then they’ll adjust the air pressure while you sleep to find the right setting to keep your airway open.

About 35% of polysomnography studies now follow this model. It saves time, money, and stress-you don’t need to come back for a second night. But it only works if the apnea is bad enough early on. If your breathing issues are mild or irregular, you’ll need a full diagnostic night first.

What Do the Results Look Like?

After your test, the raw data-sometimes over 1,000 pages of numbers and waveforms-goes to a board-certified sleep physician. They don’t just glance at it. They spend 2 to 3 hours analyzing every second of your sleep.

The final report breaks down:

• Total sleep time: How long you actually slept versus how long you were in bed.
• Sleep efficiency: Percentage of time in bed spent asleep. Below 85% is considered poor.
• Sleep stages: How much time you spent in each stage-light, deep, REM. Too little deep sleep? That’s why you feel drained.
• AHI (Apnea-Hypopnea Index): The number of breathing pauses per hour. Less than 5 is normal. 5-15 is mild, 15-30 is moderate, over 30 is severe.
• Oxygen drops: How low your blood oxygen went and how often.
• Leg movements: Number of limb jerks per hour. Over 15 may point to periodic limb movement disorder.
• Abnormal behaviors: Was there sleepwalking? Screaming? Acting out dreams?

A normal AHI is under 5. If yours is 20, you’re having 20 breathing pauses every hour-that’s one every 3 minutes. That’s not just snoring. That’s your brain waking you up to breathe. Over time, that strains your heart, raises your blood pressure, and makes you feel like you’ve been run over by a truck every morning.

How to Prepare for Your Sleep Study

You don’t need to change your life, but a few simple steps make the test more accurate:

• Stick to your normal sleep schedule for at least 3 days before the test.
• Avoid caffeine after noon on the day of your study. That includes coffee, tea, soda, and chocolate.
• Don’t nap in the afternoon.
• Wash your hair and skin-no lotions, oils, or makeup. They interfere with sensors.
• Bring your own pillow, pajamas, and anything that helps you sleep.
• Let the staff know if you take regular medications-they’ll tell you if you should skip any.

Most people worry about not being able to sleep with all the wires. But over 85% of patients get enough sleep for a valid diagnosis. The technicians are trained to help you relax. Talk to them. Ask questions. They’ve seen it all.

What Happens After the Results?

Your doctor will sit down with you and explain the findings. If you have sleep apnea, you’ll likely be prescribed CPAP therapy. If it’s narcolepsy, you might need stimulants or other medications. If you’re kicking your legs at night, iron supplements or muscle relaxants could help.

Some people need a follow-up study-like a CPAP titration if you didn’t get one during the split-night test. Others need a Multiple Sleep Latency Test (MSLT) the next day to check for excessive daytime sleepiness, especially if narcolepsy is suspected.

The key is: don’t ignore the results. Sleep disorders don’t fix themselves. Left untreated, they raise your risk of heart disease, stroke, diabetes, and depression. But treated? Many people say they feel like they’ve been given back their life.

Insurance and Costs

In the U.S., Medicare and most private insurers cover polysomnography if your symptoms meet clinical guidelines-like snoring with witnessed apneas or excessive daytime sleepiness. You’ll usually need a referral from your doctor and sometimes prior authorization.

In-lab studies cost between $1,000 and $3,000 without insurance. Home sleep tests are cheaper-$300 to $700-but they’re not always accepted by insurers if your case is complex. Many centers offer payment plans. Ask.

What’s New in Sleep Studies?

Technology is improving. New wireless sensors mean fewer wires-down from 20 to just 5 or 6. Some labs now use AI to help flag breathing events or abnormal brain patterns faster. Cloud-based systems let specialists review data remotely, speeding up diagnosis.

But the core hasn’t changed. The gold standard is still the in-lab polysomnography. It’s the only test that gives you the full picture. Home tests are great for screening. But if your life is being ruined by poor sleep, you need the full picture.