This leaflet answers common questions about having a sleep electroencephalogram (EEG). If you would like further information, or have any worries, please do not hesitate to ask the physiologist performing your test.

A physiologist will explain the EEG to you on the day of your appointment and answer any questions you may have.

What is an EEG?

A sleep EEG is a recording of electrical signals produced naturally in the brain whilst you are drowsy and asleep. This test helps us understand if there are any abnormalities with brain function and can help us see if you have a higher risk of having seizures.

What will happen during the EEG?

We start by measuring your head and then gently rub certain points on the scalp with some gel, before attaching some small metal discs to your head using a sticky paste. We use long wires to connect the metal discs to a computer to record your brain waves.

You will be asked to relax on a bed and follow instructions such as opening and closing your eyes.

You may also be asked to do a deep breathing exercise and to look at a flashing light.

We would like for you to relax and, ideally, fall asleep for a short time. A camera will take a video recording of you throughout the test. You will need to inform the physiologist prior to the EEG if you do not agree to the video recording.

The test may take up to two hours and will take place in the neurophysiology department at Royal Free Hospital on the first floor, behind clinic 2.

Before the test

Please sleep for only four hours the night before your test.

Please make sure that you are awake by 5am on the day of your test and ensure that you are tired so that there is a high possibility of you falling asleep during the test.
Please ensure that your hair is clean and free from grease, hairspray, gel, or any other hair products including weaves.

After the test

There is a potential increased risk of seizures after having too little sleep. We recommend that you are accompanied for 24 hours after your test. This includes your journey to and from hospital. Do not drive or cycle. Please take care when using public transport.

Please allow yourself to resume sleep when you return home.
The results of your test will be sent to the clinician who requested the test. We will not be able to provide a report on the day of the test as the study needs to be analysed.

Risks and side-effects

EEGs are very safe tests, which usually have minimal or no side effects.

A small number of patients have allergic skin reactions. If you are sensitive to cosmetics, lotions or sticky tape please inform the physiologist performing your test.

A small number of people are sensitive to flashing lights or deep breathing which may increase the likelihood of having a seizure. This is rare. We will discuss this with you and obtain verbal consent on the day of your test. The physiologist who monitors the EEG during the test will stop the light if you appear to be sensitive to it.