Narcolepsy Explained
Excessive Daytime Sleepiness (EDS)
Hypnogogic Hallucinations/Hypnopompic Hallucinations
Sleep Paralysis
Do I have narcolepsy?
Multiple Sleep Latency Test (MSLT)
The Nightmare by Henri Fuseli 1711



Before reading this section on Narcolepsy, you will benefit from reading the section entitled About Sleep, particularly rapid eye movement (REM) sleep. In that section, reference is made to the fact we paralyse our muscles during dreaming sleep to stop us from acting dreams out.


Narcolepsy Explained

More information on narcolepsy is available at


Narcolepsy is an intriguing condition that is explained by an understanding of sleep architecture. Our brains exist from the time we are born to the time that we die in one of three states: Wakefulness, non-REM and REM-sleep. (I am excluding the other two abnormal states of COMA and general anaesthesia here). There is a set of complex neurochemical switches in the brain that switch each state on and switch the preceding state off at the same time. Thus, we pass smoothly from one state to the next. The normal sequence through a 24 hour period from rising from sleep in the morning to rising the following morning is:

Sometimes the switching mechanism does not work as cleanly and sharply as it should, and this is the underlying problem in Narcolepsy.


Narcolepsy is an uncommon condition affecting only about 1:2000 people in the UK. There is often a long lag phase between the onset on symptom and the diagnosis being made because it is poorly understood by GPs. The actor Arthur Low was said to have suffered from it, although he was more likely to have suffered from Obstructive Sleep Apnoea (OSA) in my personal opinion.


Narcolepsy is a defect in the neurochemical switch that turns sleep on and off, and particularly REM sleep. REM sleep seems to be the dominant state, and is always trying to ‘get in on the act’ at inappropriate times. This leads to four symptoms that form the ‘Narcoleptic Tetrad’. These are:


Excessive Daytime Sleepiness (EDS)

All of us will drop off to sleep during the daytime under the right circumstances – otherwise manufacturers wouldn’t bother to make sun loungers! The exception occurs in Insomnia where the sufferer is characteristically unable to go to sleep in the daytime, however much they try and however tired they feel.


Whilst complaints of sleepiness in the daytime are common, not everyone who is prone to nap in the daytime suffers from narcolepsy. Snoring, Obstructive Sleep Apnoea and Periodic Limb Movement Disorder are much more common causes of EDS.


The sleepiness suffered by narcoleptics is very disabling. There is an overwhelming desire to drop off to sleep that the sufferer simply cannot fight off. There is a very high Epworth Sleepiness Score often close to the maximum. Naps occur at any time of the day, but sleep at night is often very fragmented with frequent awakenings and disruption. Two hypnograms are shown below. The upper one is taken from a non-narcoleptic, with a narcoleptic below, and both are recorded throughout a 24 period from 8.00 am to 8.00 am the following day. The difference is obvious, but notice that all the naps in the daytime in the case of the narcoleptic are REM sleep! REM sleep should NOT occur at the beginning of sleep, and this is another salient feature of narcolepsy and is abnormal.

24-hour ambulatory hypnogram recording

Therefore, when naps occur during the daytime, dreaming is common, and dreaming also occurs at the beginning of sleep at night time, because the narcoleptic goes straight into REM sleep, rather than non-REM sleep, which would be normal.


Hypnogogic Hallucinations/Hypnopompic Hallucinations

Because REM sleep is the dominant state, it starts almost immediately at sleep onset, and dreams occur very early in the night. Sometimes, the dreaming associated with REM can occur even just before sleep onset, and weird hallucinations occur due to the dreaming which are called Hypnogogic Hallucinations. Similarly, at the end of sleep, REM sleep may fail to switch off cleanly, and a dreamlike state may persist into waking, giving a further hallucinatory experience called a Hypnopompic Hallucination. The sufferer often feels as though there is a ‘presence’ – someone or something in the bedroom, which can be frightening. Sleep Paralysis is often associated adding to the feeling of panic.


Narcoleptics often report excessive numbers of dreams in the night, and wake up lacking refreshment from sleep when it is time to get up.


Sleep paralysis

Because REM sleep is associated with muscle paralysis to stop dream enactment, narcoleptics often wake with REM paralysis persisting in to wakefulness and a feeling that they cannot move. This is very disconcerting, especially if accompanied by a hypnopompic hallucination. Often there is a feeling of pressure on the chest, as though somebody is sitting on the sufferer, and given the feeling of a ‘presence’ in the bedroom from the hallucination, it is not difficult to understand that blind panic may occur.


Sleep paralysis can occur in non-narcoleptics too. On questioning, many people will report that they have experienced it at least once in their lives. Occasionally it occurs repeatedly in the absence of other symptoms when it is called Isolated Sleep Paralysis, and can be distressing. It may respond to tricyclic antidepressant treatment as is used for the treatment of cataplexy, but often an explanation and reassurance is all that is necessary.



Cataplexy is like sleep paralysis, but occurs suddenly during the day and when the subject is awake. Episodes of cataplexy are characterised by the onset of profound muscle weakness often triggers by emotion such as excitement, fear or shock and, most commonly, laughter. In fact, minor cataplexy is probably a normal phenomenon of unknown significance in evolution that is exaggerated in narcolepsy. This is why we have expressions in the English such as:


Weak with laughter 

Jaw dropped open with shock

Paralysed with fear


It may also explain the ‘fainting’ that occurs with bad news.


The mechanism is explained by the switching on of the paralysis of REM-sleep in isolation. The subject remains conscious and can breath, but is unable to move, and may be frightened. Typically, attacks last only a few seconds but can be longer. Not all narcoleptics suffer from cataplexy, but if there is a convincing history, it strongly supports the diagnosis of narcolepsy. Cataplexy has been shown to be more likely when levels of Hypocretin (sometimes also called Orexin) are low in the cerebral spinal fluid that surrounds the brain and spinal cord.


Do I have Narcolepsy?

Narcolepsy is an unusual cause of daytime sleepiness and sleep disordered breathing and periodic limb movements in sleep are much more common causes.


The four symptoms are quite specific and when all are present, the diagnosis may be suspected by taking an accurate medical history from the patient. To clinch the diagnosis, full overnight polysomnography is recorded in a sleep laboratory. This enables a hypnogram to be plotted, showing that REM sleep occurs very early in the night. The following day, a Multiple Sleep Latency Test (MSLT) should be performed.


Multiple Sleep Latency Test (MSLT)

An MSLT involves keeping the subject in the sleep laboratory the day following the overnight sleep study and continuing to monitor the brainwaves. At four strategic points during the day, the subject is asked to take a nap in a quiet dark room, and the time to sleep onset (Sleep Latency) is recorded from the brainwaves. Normal subjects will drop off to sleep after a latency of about 15–30 minutes, but this much shorter in the narcoleptic – typically in less than five minutes.


When these naps are recorded in narcoleptics, the hypnogram shows that REM sleep occurs, as opposed to non–REM in non-narcoleptics.


Comparative graphs between normal subjects and narcoleptics are shown below.


Notice that non-narcoleptics have a shorter sleep latency in the afternoon, a time when most of us feel a bit more lethargic, and a time when they have a siesta nap in sensible countries!

Multiple sleep latency test

The Nightmare by Henri Fuseli 1711 In 1711

Henri Fuseli painted The Nightmare. This allegorical painting probably depicts awakening from sleep with a hypnopompic hallucination and sleep paralysis.


The maiden has awoken from her slumber but lies prostrate unable to move on the chaise long. She feels pressure on her chest as though someone is sitting on her – in this case the devil, part of a hypnopompic hallucination She is also aware of the horrible surreal horse’s head with its white eyes staring through the curtains – another part of her hallucinatory vision. The whole experience must be terrifying, and is typical of a hypnopompic hallucination with accompanying sleep paralysis, two common features of narcolepsy.

The Nightmare