Polysomnography (Sleep Study)

Polysomnography (PSG) is an overnight diagnostic test that records what happens in your body while you sleep, helping doctors identify the cause of a sleep disorder.

During the study, sensors placed on your skin and scalp continuously measure brain activity, eye movements, muscle activity, heart rhythm, breathing effort, airflow through your nose and mouth, blood oxygen levels, and body position. None of the sensors go inside your body. The data is recorded as you sleep naturally in a monitored room, and a specialist then analyses the recordings to see whether your sleep is being disrupted and, if so, why.

PSG is ordered when a doctor suspects that a patient's symptoms are caused by a problem that occurs specifically during sleep. It is most commonly used to investigate breathing-related sleep disorders, but it also helps diagnose several other conditions.

• Obstructive sleep apnoea (OSA) — repeated episodes where the throat closes during sleep, briefly stopping breathing
• Central sleep apnoea — episodes where the brain temporarily fails to send the correct signals to the breathing muscles
• Hypopnoea — episodes of very shallow breathing that reduce oxygen levels during sleep
• Periodic limb movement disorder — repetitive leg or arm movements that interrupt sleep
• Narcolepsy — a condition causing sudden, uncontrollable episodes of sleepiness during the day
• REM sleep behaviour disorder — acting out dreams physically, sometimes violently, during sleep
• Unexplained excessive daytime sleepiness that has not been explained by other tests
• Parasomnias (unusual sleep behaviours) such as sleepwalking or night terrors
• Nocturnal seizures (epileptic episodes that happen during sleep)

PSG is generally not needed in every person who snores or sleeps badly. Your doctor will decide based on your symptoms, medical history, and the results of simpler screening tools such as questionnaires or home sleep tests.

Because PSG is a recording test with no instruments entering the body, it carries very little risk. Most people experience only minor discomforts related to wearing the sensors overnight.

• Skin irritation or mild redness where adhesive sensors or electrode gel was applied — this usually fades within a day
• Difficulty falling asleep or sleeping less soundly than usual because of the unfamiliar environment and attached sensors
• Slight scalp itching from the conductive gel used to attach EEG (brain-wave recording) electrodes — this washes out easily
• Rarely, a small skin scratch if a sensor comes loose and is re-applied during the night
• If supplemental oxygen or CPAP (a device that keeps the airway open with gentle air pressure) is trialled during the study, mild throat or nasal dryness may occur

Preparation for PSG focuses on making sure your sleep that night reflects your usual sleep patterns as closely as possible. Your sleep clinic or hospital will give you specific instructions, but the following points apply in most centres.

In the days before the study, most centres ask patients to avoid caffeine (coffee, tea, energy drinks, cola) from the afternoon or earlier on the day of the test, and to avoid alcohol entirely, since both change how your sleep is structured. If you take sleeping tablets or sedatives, your doctor will advise whether to continue or pause them — do not change these yourself. Smokers are usually asked to avoid smoking for several hours before arriving, as nicotine affects breathing patterns during sleep.

Before the study, your doctor will usually review your medical history and sleep symptoms, and may ask you to complete a sleep diary or questionnaire for one to two weeks beforehand. No specific blood tests or imaging are required before a standard PSG, though these may have already been done as part of your overall assessment.

On the day itself, you will typically arrive at the sleep laboratory in the early evening. The procedure usually follows these steps:

• You arrive, change into comfortable sleepwear, and a technician explains what will happen during the night.
• The technician applies sensors to your scalp, face, chest, abdomen, and legs using adhesive patches or gel. This takes roughly 30 to 60 minutes and is not painful.
• Thin belts are placed around your chest and abdomen to measure breathing effort.
• A small clip called a pulse oximeter (a sensor that measures blood oxygen and pulse) is placed on one finger.
• A soft cannula (a small tube) is positioned just below your nostrils to detect airflow, or small sensors are placed near your nose and mouth.
• The technician checks that all sensors are recording correctly before you settle into bed.
• You are asked to try to sleep at your usual bedtime. The room is kept dark and quiet.
• A technician monitors the recordings throughout the night from an adjacent room and may briefly re-attach any sensor that comes loose.
• You wake up naturally or at a set time in the morning. The sensors are removed, and you can shower and leave.

Because PSG is a diagnostic recording test and not a surgical procedure, there is no physical recovery period. Most people can go straight to work or their normal activities after leaving the sleep laboratory in the morning, though some feel tired if they slept less well than usual in the unfamiliar setting.

• Any gel residue from the scalp electrodes can be washed out with normal shampoo after leaving the laboratory.
• Mild skin redness at sensor sites usually resolves on its own within 24 hours; if it persists or becomes itchy, let your doctor know.
• There are no wound care requirements, activity restrictions, or dietary restrictions after a standard PSG.
• Results are not usually given on the same night. A specialist analyses the full night's recording, which typically takes several days to a few weeks depending on the centre.
• Your doctor will schedule a follow-up appointment to discuss the findings and, if a sleep disorder is confirmed, to explain what treatment options are available.
• If CPAP therapy or another device was trialled during the study and is recommended, your care team will arrange fitting and instruction separately.
• Keep any sleep diary you were given going until your follow-up appointment, as your ongoing sleep notes may help your doctor interpret the results.