Sleepiness, fatigue and alertness...

Sleepiness - Fatigue - Vigilance - Normal or pathological sleepiness - Severity of the disorder


Sleepiness is the desire to sleep. It is a normal biological phenomenon. Sleepiness leads to sleep, just as hunger leads to food.

However, drowsiness can be excessive: the risk of falling asleep is high and frequent, including in situations and at times when sleep is not appropriate.

drowsiness precedes sleep

excessive sleepiness


Sleepiness and fatigue are not synonymous.

Acute fatigue

Acute fatigue is usually induced by excessive activity.
It is often reversible after rest. A distinction is made between physical fatigue, characterised by a lack of energy and exhaustion, and mental fatigue, characterised by a lack of motivation, desire or interest.

Excessive fatigue

It is an irresistible, overwhelming fatigue, a real state of sustained exhaustion, with a decrease in physical and mental capacity. Excessive fatigue can be chronic. It is often associated with a pathology. It cannot be reversed by rest or sleep.

physical fatigue

psychological fatigue


Vigilance is the ability of the central nervous system to respond effectively to a stimulus or event, through the mobilisation of cognitive and behavioural resources.
Alertness may be impaired by excessive sleepiness but also by a state of hyperarousal.

Normal or pathological sleepiness

ordinary sleepiness

Pathological sleepiness is characterised by the following:

  • Irritability, disinhibition
  • Decreased motivation, decreased productivity
  • Alteration of the frontal lobe :
    • Apathy, decreased verbal fluency
    • Attention deficit, memory impairment
    • Impaired judgment and reasoning
  • Intrusion of drowsiness :
    • Periods of micro-sleep (5-10 seconds) that lead to attention problems
    • Continuous sleep

Severity of the disorder

These sometimes irrepressible and inappropriate sleep attacks can have embarrassing or even dramatic consequences on the life of the subject. They disrupt the quality of life of the patient and those around him and can even prevent any professional activity due to the risk of accidents at work and in traffic.

example of consequences of pathological sleepiness