Excessive daytime sleepiness can occur for a number of reasons. For many people, feelings of tiredness can be attributed to not getting enough sleep at night, but several sleep disorders can also cause daytime sleepiness.

Sleep deficiency and daytime sleepiness may lead to negative outcomes at work or school. People who experience sudden tiredness during the day but are awake at night may struggle with focusing at work, making decisions, and managing their emotions. Daytime sleepiness also poses an increased risk of being involved in an accident on the road. Thankfully, there are measures you can take to mitigate daytime sleepiness and get enough sleep each night.

Why Does Daytime Tiredness Occur?

Daytime sleepiness is typically a symptom of certain sleep disorders, which can impact sleep quality and how much sleep a person gets each night. It is important to note that daytime tiredness is different from fatigue. Fatigue refers to a lack of energy or motivation that may occur due to lack of sleep, but can also stem from other factors like emotional stress or boredom. 

Obstructive Sleep Apnea 

Obstructive sleep apnea is a disorder characterized by a restriction or blockage to the upper airway that causes people to choke or gasp for air in their sleep, often waking up in the process. Obstructive sleep apnea can also cause heavy snoring that disrupts sleep and makes people and their sleeping partners feel tired the next day.


Narcolepsy is defined as the overwhelming urge to sleep during the day, which in turn can interfere with nightly sleep. During “sleep attacks,” some people with narcolepsy experience cataplexy, or the sudden loss of muscle tone that causes them to fall or slump over as they nod off. Excessive daytime sleepiness is considered the hallmark symptom of narcolepsy.


Hypersomnia is another condition that causes people to feel excessively tired suddenly during the day. Unlike narcolepsy, hypersomnia does not cause sleep attacks and cataplexy will not occur. Many people with this condition have idiopathic hypersomnia, meaning the cause is not known.

Delayed Sleep-Wake Phase Disorder (DSWPD)

People with delayed sleep-wake phase disorder feel tired later in the evening compared to other people, and may wake up later as a result. It occurs when a person’s circadian rhythm, guiding their sleep-wake schedule, is not aligned with each day’s natural light and darkness cycles. Those who attempt to correct their delayed sleep-wake phase may experience excessive sleepiness the next day.

Non-24-Hour Sleep-Wake Rhythm Disorder 

The circadian rhythms of most adults will reset every 24 hours in order to align with daylight and darkness. For people with non-24-hour sleep-wake rhythm disorder, circadian rhythms are not cycling on a 24-hour basis. Excessive daytime sleepiness is considered a chief symptom of non-24-hour sleep-wake rhythm disorder.

Shift Work Disorder 

Shift work disorder affects people whose jobs require them to work late at night or early in the morning, and sleep during the day. This circadian rhythm condition can cause excessive daytime or nighttime sleepiness, depending on when the person works, and also cause sleep disruptions during their allotted rest time.

Other Disorders and Additional Factors

Another disorder known as insufficient sleep syndrome occurs when people persistently fail to get enough sleep at night due to factors such as family responsibilities or a work schedule that requires early rising. Sudden tiredness during the day often occurs as a result. 

The most commonly diagnosed sleep disorder – insomnia – does not necessarily cause excessive daytime sleepiness. People with insomnia usually experience fatigue from being unable to sleep, rather than feelings of excessive tiredness that compel them to sleep. 

Apart from sleep disorders, other factors can cause sudden tiredness during the day. Jet lag, a circadian rhythm condition that affects travelers adjusting to their current time zone, can make people very tired during the day. Sedative medications are also known to cause daytime tiredness. Additionally, some research suggests that excessive sleepiness may be genetically inherited .

How Much Sleep Do You Need?

Adults generally need at least seven hours of sleep each night. Surveys have found that nearly one-third of adults in the U.S. reported getting less than seven hours of nightly sleep on a regular basis. Since a good night’s rest is essential for bodily recovery and repair , those who do not get enough sleep on a regular basis are at higher risk for certain disorders , including high blood pressure, cardiovascular disease, obesity, diabetes, and depression.

The amount of sleep you should get each night will evolve over the course of your life.

Age GroupAge RangeRecommended Amount of Sleep per Day
Infant4-12 months12-16 hours (including naps)
Toddler1-2 years11-14 hours (including naps)
Preschool3-5 years10-13 hours (including naps)
School-age6-12 years9-12 hours
Teen13-18 years8-10 hours
Adult18 years and older7 hours or more

If you feel tired during the day after a night without enough sleep, you may be able to alleviate your tiredness by simply getting more rest. Another remedy may be improving your sleep hygiene by going to bed and waking up at the same times each day, avoiding caffeine in the afternoon and evenings, and maintaining a relaxing bedroom environment.

However, persistent feelings of excessive daytime tiredness may warrant a doctor’s visit, especially if you regularly sleep for the recommended amount of time each night.

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9 Sources

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