What happens during an overnight sleep study
A step-by-step look at arrival, sensors, what is recorded, what to bring, split-night studies and getting results.
An overnight sleep study, or polysomnography, records how your body behaves during sleep. If you have one scheduled, knowing the routine can make the night easier. Details vary by facility, so follow the instructions you are given. This guide is general information, not medical advice.
Why a study is ordered
Clinicians order sleep studies to evaluate problems such as suspected sleep apnea, unusual movements or behaviors during sleep, or excessive daytime sleepiness. The National Heart, Lung, and Blood Institute (NHLBI) describes the study as non-invasive and painless. Your doctor decides whether a lab study or a portable home test fits your situation.
Arrival and setup
You typically arrive in the evening at a sleep center, often set up like a quiet bedroom. A sleep technologist explains the process, may ask about your usual sleep habits and medications, and then applies the sensors. Setup can take a while, so ask the staff what to expect. Most facilities have a way for you to contact the technologist during the night, and you can generally ask to use the bathroom, since sensors can be temporarily disconnected.
What is measured
According to NHLBI, removable sensors are placed on the scalp, face, eyelids, chest, limbs and finger. Together they record brain waves, heart rate, breathing effort and rate, oxygen levels and muscle movements before, during and after sleep. In practical terms:
- Scalp and face sensors show sleep stages and when you wake.
- Belts around the chest and abdomen show breathing effort.
- A sensor near the nose and mouth tracks airflow.
- A clip on the finger tracks blood oxygen.
- Leg sensors detect limb movements.
- Heart rhythm is recorded, and many labs also record snoring sound and body position.
The AASM patient site, sleepeducation.org, has additional plain-language descriptions of sleep testing. There is a small risk of skin irritation from the sensors, which resolves after removal, per NHLBI.
What to bring
- Comfortable pajamas and any items that help you sleep, such as your own pillow, if the facility allows it
- A list of your medications, and your medications for the evening and morning
- Toiletries and a change of clothes for the next day
- Something quiet to read before lights out
- Your insurance card, photo ID, and any paperwork the facility requested
Interpreters and disability access
If you need a spoken-language or sign language interpreter, large print or other help because of a disability, tell the center when you book. Under HHS's rule for health programs that receive federal financial assistance (45 CFR part 92), language assistance must be free of charge and provided by a qualified interpreter, and the program may not rely on a minor child to interpret except briefly in an emergency. Auxiliary aids and services for people with disabilities must also be free, timely and in an accessible format. If a family member or caregiver needs to stay with you overnight, arrange that in advance, since policies vary by center.
What to avoid and prepare
Ask the center for its specific instructions. Facilities commonly ask patients to keep hair clean and free of oils, gels or sprays and to avoid lotions on the skin where sensors go, because these can affect how sensors stick. Many also ask you to limit caffeine or alcohol later in the day and to avoid unscheduled naps on the day of the study. Do not stop or change prescribed medicines unless your doctor tells you to. If you use a CPAP, a dental appliance or a mobility aid, or need help with care needs, tell the facility in advance.
Sleeping in a lab
Many people worry they will not sleep well. It is common to sleep less than usual, but a study often gathers enough information anyway. If you have trouble, tell the technologist, who can help but cannot promise a particular outcome.
Split-night studies
Some facilities use a split-night protocol. If clear signs of significant sleep apnea appear in the first part of the night, the technologist may wake you to fit a PAP mask and begin adjusting air pressure for the rest of the night. This allows diagnosis and initial pressure setting in a single visit. Whether this is done depends on your findings and on facility and insurer policies, so ask ahead. If it is not done, a second night for pressure titration may be scheduled.
In the morning
Staff remove the sensors and you can usually leave early in the morning. Ask for a work note if you need one. Skin marks or a little adhesive residue are common; washing your hair and skin usually handles this.
Results and follow-up
After the study, the recording is scored by a technologist and reviewed by a physician who combines it with your history. The doctor then creates a treatment plan for any disorder identified, according to NHLBI. The timing of results varies by facility and physician schedule; ask at check-in how you will be told and who will explain the findings. Results may come at a follow-up visit or by phone or portal. If you have not heard back after the time you were given, contact the office.
You can ask for a copy of the sleep study report for your own records or for another clinician. Under the HIPAA Privacy Rule, a covered provider must act on your request within 30 days, with one 30-day extension allowed, and may charge only a reasonable, cost-based fee for copies (45 CFR 164.524). If the study leads to PAP treatment, our treatment and coverage guide explains the follow-up visit and usage records Medicare looks for in the first three months.
When to see a doctor
Do not wait for a study appointment if you have chest pain, severe shortness of breath or fall asleep dangerously, such as while driving; seek urgent care. Otherwise, the CDC suggests seeing a health care provider if you regularly have trouble sleeping or notice signs of a sleep disorder. Untreated sleep conditions are linked to health risks such as high blood pressure, heart failure, stroke and diabetes, per NHLBI, which is why follow-up matters.
General information only, current as of the date above. The information on Sleep Clinic Index is not medical advice and does not replace a doctor, nurse, discharge planner or other qualified professional. Do not use it to make decisions about diagnosis or treatment. If you have a medical emergency, call 911. Rules and programs change; check the official sources linked in this guide.