What Happens During a Sleep Study?
Reviewed by our editorial team
Last updated: 2026-04-01
Quick Answer
During an in-lab sleep study, sensors attached to your body monitor brain waves, breathing patterns, oxygen levels, heart rate, and limb movements throughout the night — all analyzed to diagnose sleep disorders.
A sleep study — formally called a polysomnography (PSG) — is the gold-standard diagnostic test for sleep disorders. Despite what many people imagine, it is not uncomfortable or frightening. Sleep labs are designed to be as similar to a hotel room as possible, and most people sleep adequately enough to generate useful data.
Sleep studies are most commonly ordered to diagnose obstructive sleep apnea, but they are also used to diagnose narcolepsy (via a Multiple Sleep Latency Test), REM sleep behavior disorder, periodic limb movement disorder, and complex parasomnias. Understanding what happens can help reduce anxiety and improve cooperation, which leads to better results.
What You Will Experience
You will arrive at the sleep lab in the evening — typically around 8–9pm. A sleep technician will greet you and show you to your private room, which typically has a comfortable bed, a private bathroom, and lighting you can control. Before you sleep, the technician will apply a series of sensors to your body using mild adhesive or tape: electrodes on the scalp, face, and legs, plus a pulse oximeter on a finger, breathing belts around the chest and abdomen, a nasal cannula to detect airflow, and EKG leads on the chest.
The application takes 30–60 minutes and is not painful. The wires are bundled together and connected to a bedside box, giving you enough slack to move comfortably and use the bathroom if needed. The technician monitors everything from an adjacent room via a closed-circuit camera and can communicate with you through an intercom.
What the Study Measures
The EEG (electroencephalogram) data records brain electrical activity and allows the sleep scorer to identify sleep stages: N1 (light), N2, N3 (deep slow-wave sleep), and REM. This staging reveals whether you are getting adequate deep and REM sleep, and when arousals occur. Respiratory monitoring detects apneas and hypopneas, measuring how often they occur per hour — this is the apnea-hypopnea index (AHI), which determines sleep apnea severity.
The pulse oximeter continuously records blood oxygen saturation, revealing how much oxygen desaturation accompanies each breathing event. Leg movement sensors detect periodic limb movements. The video recording is often reviewed alongside the data to correlate behavioral observations with physiological findings — this is especially important for diagnosing parasomnias like sleepwalking or REM sleep behavior disorder.
After the Study
In the morning — typically around 6am — the technician will remove all sensors and you can shower and dress. The raw data is scored and analyzed by a trained sleep technologist, then interpreted by a sleep medicine physician who writes a formal report. This process typically takes 1–2 weeks.
Results are communicated at a follow-up appointment where the physician explains the findings and recommends treatment. If sleep apnea is diagnosed, a CPAP titration study may be scheduled — or auto-adjusting CPAP may be prescribed directly. If the initial study was inconclusive, an in-lab follow-up may be arranged.
Frequently Asked Questions
References
- [1]American Academy of Sleep Medicine. Clinical Guidelines for Polysomnography.
- [2]Mayo Clinic. Polysomnography (Sleep Study): What You Can Expect.
The information on this page is for educational purposes only and is not a substitute for professional medical advice. Always consult a qualified healthcare provider for diagnosis and treatment.