Normal sleep

In humans, a normal night of sleep is usually characterized by a succession of slow sleep sleep (or non-REM sleep for non-rapid eye movement) and REM sleep (REM for rapid eye movement). These REM and non-REM sleep cycles are usually repeated 4 to 6 times during the night. During non-REM sleep, we distinguish three stages: N1 (light sleep), N2 (slow sleep) and N3 (slow deep sleep). They are named according to certain physiological characteristics including variations of the frequency and the amplitude of brain waves recorded with electroencephalography (EEG). REM sleep, on the other hand, is characterized by the appearance of cerebral activity similar to what is observed during wakefulness; it is often referred as paradoxical sleep for that reason. It is also during REM sleep that we experience muscle atony (paralysis of the muscles) as well as rapid eye movements. Dreams are often most intense and detailed during REM sleep.

Figure legend: This is a hypnogram depicting a healthy young adult’s night of sleep. Stages N1, N2, and N3 are followed by a period of REM sleep (blue boxes). This sequence is repeated 4 to 6 times during the night.

Many differences are observed between individuals with normal sleep. For example, the number of hours it takes for each person to recover and feel rested the next day varies greatly. However, experts recommend getting 7-9 hours of sleep per night on a regular basis. Sleep also changes with age. In fact, the need for sleep is much greater in children and adolescents, while in the elderly, the sleep episode may be shorter, more fragmented and lighter.

During sleep, there are not only significant changes in brain activity, but also changes in muscle activity, hormonal secretion, autonomic nervous system activity, body temperature, as well as a multitude of metabolic, cellular, and molecular changes.

Sleep disorders

At least 25% of the population suffers from a sleep disorder requiring the intervention of a healthcare professional. Having poor sleep not only makes the nights uncomfortable but can affect the quality of the day (being more irritable, having problems concentrating, being drowsy).

Fortunately, most sleep disorders can be attenuated or sometimes even erased with a good diagnosis and treatment by sleep specialists.


Insomnia is a sleep disorder characterized by a set of symptoms related to a decrease in sleep duration that occurs more than 3 nights per week. Initial insomnia is characterized by difficulty falling asleep and therefore, people with this type of insomnia has a very long sleep latency. A very early awakening in the morning is called terminal insomnia. Maintenance insomnia is a difficulty in maintaining sleep and is therefore characterized by numerous and / or prolonged awakenings during the night. Some people have the impression that they get little or no sleep all night, although their sleep duration is normal when measured in the laboratory. This type of insomnia is paradoxical insomnia. Their brains may stay more active during sleep, making it seem like they are not sleeping. Sometimes a combination of different types of insomnia can be found in one person. Insomnia has adverse daytime consequences such as fatigue and drowsiness, changes in mood and irritability, disturbances in attention and concentration as well as impaired psychomotor performance.

The diagnosis is made when these sleep problems interfere with a person's functioning during the day (e.g., difficulty concentrating, irritability, etc.). It is therefore not only the short duration of sleep that is important for the diagnosis, but also the consequences of poor sleep on daytime well-being. Cognitive behavioural therapy is particularly effective in improving insomnia. It helps to restore good behaviour to better appreciate the hours spent in bed.


Hypersomnia refers to sleep disorders that are characterized by excessive daytime drowsiness despite having sufficient sleep during the night. This disorder usually starts in teenagers or young adults. Patients with hypersomnia have bouts of sleep during the day, unwittingly long naps (sometimes over an hour) which are usually not restorative. These patients experience sleepiness, are difficult to wake up, and waking up is associated with confusion. Idiopathic hypersomnia (without a known cause) is distinguished from secondary hypersomnia associated with a physiological problem such as restless legs syndrome or sleep apnea.


Narcolepsy is a disorder characterized by sudden bouts of sleep during the day. Patients may experience cataplexy as well as, in some cases, sleep paralysis and hypnagogic hallucinations. Cataplexy is defined by a loss of muscle tone without alteration of consciousness and is triggered by strong emotions such as anger, joy, laughter, fear. Narcolepsy is distinguished from idiopathic hypersomnia by the restorative effect of naps, sudden bouts of short-lived sleep and sleep onset in REM sleep.

Behavioural disorder in REM sleep (REM sleep disorder).

REM sleep disorder appears mainly after the age of 50 and is clinically characterized by complex and often violent motor activities (kicking, punching, flight behaviour) during sleep. In these patients, there is a loss of muscle atonia, which is usually present during normal REM sleep. These behaviours can result in injury to the patient himself or his bed partner. Several longitudinal studies, including those by Drs. Montplaisir, Gagnon and Postuma, have shown that patients with idiopathic REM sleep disorder can develop Parkinson's disease or other dementia such as Lewy body dementia within 10 years of being diagnosed with this sleep disorder.


Although significantly more common in children, sleepwalking affects 2% to 4% of adults. Sleepwalking usually occurs during the first third of the night, when sleep is deeper. The behaviours that occur during an episode vary from simple behaviours, such as sitting in bed or pointing at an object, to very complex activities such as cooking, playing a musical instrument, or driving a car. Typically, the sleepwalker has his eyes open and can interact more or less consistently with other people in the room. It must be said that sleepwalkers exhibit disturbed judgment and altered state of consciousness as well as an erroneous perception of the environment, which can lead to funny or sometimes dangerous situations. Contrary to popular belief, it is not dangerous to wake a sleepwalker during an episode. However, it is always best to advise the sleepwalker to gently get to bed, as waking up suddenly during an episode may be associated with confusion or restlessness.

Sleep Apnea

More than 20% of middle-aged adults and almost 50% of people over 65 have symptoms of sleep apnea. We talk about sleep apnea when a person stops breathing for at least 10 seconds and repeatedly throughout the night. Most sleep apneas occur when the airways are blocked. This condition causes short but frequent awakenings during the night resulting in a decrease in sleep quality. This leads to daytime sleepiness, headaches and dry mouth upon awakening, changes in mood and irritability. In the long term, patients suffering from this problem experience cognitive deficits of different types: impaired general intellectual functioning, attention, alertness, memory, executive functions as well as their manual dexterity. They are also at risk of developing cardiovascular complications. Effective treatments are offered through continuous positive airway pressure devices, dentures, surgery, or weight loss.

Restless Legs Syndrome

Is Restless Leg Syndrome Partly Genetic? In Quebec, a high percentage of the population has this disorder, and it is in part due to our genes! Restless Leg Syndrome is a disorder characterized by an overwhelming urge to move the lower, and sometimes upper, limbs associated with paresthesias, motor restlessness, increased symptoms at rest with relief from activity, and increased symptoms in the evening and / or during the night. This disorder causes difficulty falling asleep as well as frequent awakenings during the night. Walking generally helps to reduce discomfort momentarily. If the symptoms are severe, pharmacological treatment can be used to reduce symptoms and allow better sleep.

Periodic Leg Movement during Sleep (PLMS)

PLMS syndrome is characterized by the repeated, rhythmic onset (often every 20 to 40 seconds) of short duration leg movements. The most common sleep complaints in patients with PLMS consist of non-restful sleep and daytime sleepiness since these periodic movements cause short arousals fragilizing sleep depth.

Circadian Disorders

An internal biological clock located in the centre of our brain manages all of our physiological behaviours and activities on a 24-hour schedule. This is the case, of course, with our sleep-wake cycle. The internal clock is greatly influenced by the light that reaches our eyes. This is why people who are blind are more at risk of developing a biological rhythm disorder. These sleep disorders refer those with misalignment to the light-dark cycle. They can be either of environmental origin (irregular hours, rotating work, jet lag) or of internal origin (clock dysfunction. biological, blindness, special neurological condition). People with 24-hour arrhythmia have difficulty sleeping at night and staying awake during the day. Circadian disorders include advanced phase syndrome, delayed phase syndrome, irregular or different 24-hour sleep-wake syndrome, and night-shift worker sleep disorders.

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