Someone may fall asleep randomly for several reasons, most commonly due to a lack of sleep. Certain conditions may also make a person fall asleep randomly, including kidney disease and thyroid disorders.

In this article, we explore the reasons for falling asleep randomly, looking at various lifestyle, environmental, and medical factors.

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Some lifestyle factors can cause someone may fall asleep randomly, including the below.

Sleep habits

The most common reason a person may fall asleep randomly is not getting enough sleep. Many people need 7–9 hours of sleep each day, and when an individual does not get enough, their body may force them to fall asleep to catch up.

Some bedtime lifestyle habits can disrupt a person’s sleep, including:

  • not going to bed at the same time each day
  • using electronic devices before bed
  • having large meals before bed can disrupt sleep

Making a regular sleep schedule and routine and sticking to it usually helps improve sleep quality.

Alcohol and illegal drug use

Alcohol consumption can reduce sleep quality. The use of illegal drugs, such as cocaine and amphetamines, can also disrupt someone’s sleep cycle. Avoiding the use of illicit substances will normally help improve sleep.

Night-shift work

According to some estimates, 22.3% of night-shift workers feel overly tired during the day, with 18.5% experiencing insomnia. This is likely because working through the night and sleeping during the way goes against the normal human sleep-wake cycle.

The below environmental factors may also impact sleep and cause someone to fall asleep randomly.

Noise pollution

Trying to sleep with noise from buses, trains, trucks, honking cars, construction, and other sounds can be difficult. Even otherwise pleasant sounds, such as from animals, can disrupt sleep during the late or early morning hours.

These types of noises, called environmental noise or noise pollution, may significantly reduce sleep quality over time.

To cover or distract from noise pollution, try using earbuds or a white noise machine.

Warm or cold environments

The body’s internal body temperature and the temperature of the environment strongly regulate sleep, and being too hot or cold can interfere with sleep. However, everyone has different temperature preferences. Some research suggests it is best to keep bedrooms between 66–70°F (18.8–21.1°C) while sleeping.


The body’s sleep-wake cycle has strong links with the sun’s daily cycle. Exposure to light 2 hours before bedtime or during sleep can change when the body starts to feel sleepy. It can also be difficult to fall and stay asleep in bright environments. If light interference is a problem, try using items that can block light, such as blackout curtains or eye masks.

Medical conditions may also impact sleep and cause a person to fall asleep randomly. We explore some below.


People with insomnia have a hard time staying or falling asleep. They may also wake up very early and be unable to fall back asleep.

One of the most common daytime symptoms of insomnia is being very drowsy during the day. Doctors treat this condition by addressing its underlying cause, reinforcing good sleep hygiene, and recommending sleep-promoting adjustments to a person’s routine.

Obstructive sleep apnea

People with obstructive sleep apnea (OSA) have difficulty getting air into the lungs due to an obstruction in the upper airway. A person with OSA often makes snorting or gasping noises periodically while sleeping. These gasps and snorts disrupt sleep, which can result in waking up several times. Treatment for OSA involves clearing the obstruction, usually by using continuous positive airway pressure devices.

Restless legs syndrome

Restless legs syndrome (RLS), or Willis-Ekbom disease, is a common sleep-related movement disorder. A person with RLS has an often unpleasant or uncomfortable urge to move their legs during periods of inactivity, particularly in the evenings. RLS is a treatable condition that generally responds well to medicines, which aim to reduce or eliminate symptoms and improve daytime function, sleep, and quality of life.

Electrolyte imbalances

Imbalances in important electrolytes, such as sodium, potassium, calcium, phosphate, and magnesium, can cause someone to feel extremely tired. Electrolytes are minerals that carry electrical charges and are essential for several vital bodily processes. People can treat electrolyte imbalances by following a balanced and healthy diet.


Anemia occurs when the body does not have enough hemoglobin, a type of protein that helps red blood cells carry oxygen from the lungs to bodily tissues. People with anemia often feel exhausted all the time. While there are many different causes for this condition, treatments always involve addressing the underlying cause.


Depression can disrupt someone’s sleep, making them unable to sleep properly or sleep too much. Treatment involves psychotherapy and medications such as antidepressants, while alternative therapies may include meditation, acupuncture, or light therapy.

High or low blood sugar levels

Changes in blood sugar (glucose) levels can impact sleep. When these levels are too high, a person may become irritable and too warm. They may also need to wake up to urinate multiple times as they sleep. Additionally, high blood sugar levels can make someone feel very sleepy during the day.

Having low blood sugar levels during sleep can also cause disruptions, making it difficult to wake up and causing excessive daytime drowsiness.

Diabetes can often lead to variations in blood sugar, metabolic syndrome, or other metabolic diseases. Most people can control their blood sugar levels with lifestyle modifications and medications.

Thyroid disorders

Thyroid disorders often seem to cause sleep problems, likely due to changes in thyroid secreting hormone (TSH) levels. A 2019 study found thyroid disorders increased how long it took to fall asleep, reduced sleep, and increased sleep disruptions. People with thyroid disorders may require lifestyle changes to control the activity of their thyroid and TSH levels.

Kidney disease

People with chronic kidney disease (CKD) tend to experience a reduction in sleep quality and an increased rate of sleep disorders. However, it is still not clear exactly why the condition causes sleep problems. Treatment options for CKD often involve lifestyle changes and medications.


Narcolepsy is a brain disorder that makes a person feel sleepy most of the time. People with the condition sometimes fall asleep suddenly, sometimes unexpectedly. They can even fall asleep in the middle of activities, such as eating, talking, or driving.

Individuals usually develop narcolepsy during their teens or early 20s, although some may develop earlier or later in life. Once it starts, the disorder can make it hard to do work, schoolwork, or other activities.

Several types of prescription and over-the-counter medications can cause excessive daytime drowsiness, including:

  • pain medications
  • antidepressants
  • medications for attention-deficit hyperactive disorder
  • antiepileptics, seizure medications
  • antianxiety medications
  • antihistamines, allergy medications
  • sedatives
  • antipsychotic medications for treating psychosis

If sleepiness or randomly falling asleep impacts someone’s life significantly, a doctor may prescribe different medications or advise someone to stop taking certain medications.

The most common cause of falling asleep randomly during the day is not getting enough good quality sleep. But a range of medical conditions, environmental factors, lifestyle factors, and medications can also be responsible.

Speak with a doctor if randomly falling asleep interferes with daily activities or becomes dangerous. In most cases, the cause of daytime sleepiness can be treatable with lifestyle changes, behavioral therapies, or medications.