Somnolence (alternatively sleepiness or drowsiness) is a state of strong desire for sleep, or sleeping for unusually long periods (compare hypersomnia). It has distinct meanings and causes. It can refer to the usual state preceding falling asleep, the condition of being in a drowsy state due to circadian rhythm disorders, or a symptom of other health problems. It can be accompanied by lethargy, weakness and lack of mental agility.

In psychology, sleepiness refers to the state of feeling drowsy or fatigued, often accompanied by a desire to sleep. Sleepiness can be caused by a variety of factors, including lack of sleep, irregular sleep patterns, certain medications, and certain medical conditions.

Examples of sleepiness in psychology include:

  • A college student who is feeling sleepiness during class because they stayed up late studying for an exam the night before.
  • A shift worker who is feeling sleepiness during their evening shift because their body is used to sleeping at that time.
  • A person with insomnia who is feeling sleepiness during the day because they are not getting enough sleep at night.

Sleepiness can also be a symptom of a sleep disorder such as sleep apnea, insomnia, or narcolepsy. In these cases, the individual may experience excessive sleepiness during the day despite getting enough sleep at night.

Prolonged or excessive sleepiness can have negative effects on an individual's physical and mental health, as well as their ability to function in daily life. It can lead to cognitive impairment, decreased productivity, and accidents. So, getting enough good quality sleep and maintaining regular sleep patterns are important for overall well-being.