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What causes drowsiness? 45 possible conditions

What Is Drowsiness?

Feeling abnormally sleepy or tired during the day is commonly known as drowsiness. Drowsiness may lead to additional symptoms, such as forgetfulness or falling asleep at inappropriate times.

What Are the Causes of Drowsiness?

A variety of things may cause drowsiness. These can range from mental states and lifestyle choices to serious medical conditions.

Lifestyle Choices

Certain lifestyle choices may lead to increased drowsiness, such as working very long hours or switching to a night shift. In most cases, your drowsiness will reduce as your body adapts to your new schedule.

Mental State

Drowsiness can also be a result of your mental, emotional, or psychological state

Depression can greatly increase drowsiness, as can high levels of anxiety or stress. Boredom is another known cause of drowsiness. If you are experiencing any of these mental conditions, you’re also likely to feel fatigued and suffer from apathy.

Medical Conditions

Some medical conditions can cause drowsiness. The most common is diabetes. Other conditions that may lead to drowsiness include those that cause chronic pain or affect your metabolism, such as hyponatremia (when the level of sodium in your blood is too low), or hypothyroidism. Finally, infectious mononucleosis (Mono) and chronic fatigue syndrome (CFS) are other well-known causes of drowsiness.


Many medications, particularly antihistamines, tranquilizers, and sleeping pills, list drowsiness as a possible side effect. These medications carry a warning against driving or operating machinery while consuming these drugs.

Talk to your doctor if you suffer from prolonged drowsiness due to your medications. They may prescribe an alternative or adjust your current dosage.

Sleeping Disorder

Excessive drowsiness without a known cause can be a sign of a sleeping disorder. There’s a range of sleeping disorders, and each has its own unique effects.

Sleep apnea is a disorder where a blockage in your upper airways creates pauses in your breathing throughout the night, causing you to wake up frequently with a choking sound. Other sleep disorders include narcolepsy, restless leg syndrome, and delayed sleep phase disorder.

How Is Drowsiness Treated?

Treatment of your drowsiness will depend on its cause.


Some drowsiness can be treated at home, especially if it’s the result of life choices, like working longer hours, or a mental state such as stress.

In these cases, it may help to get plenty of rest and to distract yourself. It’s also important to investigate what’s causing the problem, such as stress or anxiety, and take steps to reduce the feeling.

Medical Care

During your appointment, your doctor will try to identify the cause of your drowsiness by discussing the symptom with you. They may ask about how well you sleep, and whether you wake up frequently in the night.

Be prepared to answer questions about:

  • your sleeping habits
  • the amount of sleep you get
  • if you snore
  • how often you fall asleep during the day
  • how often you feel drowsy during the day

Your doctor may ask you to keep a diary of your sleeping habits for a few days, documenting how long you sleep at night and what you’re doing when you feel drowsy in the day. They may also ask for specific details, such as if you actually fall asleep in the day and whether you wake up feeling refreshed.

If the doctor suspects that the cause is psychological, they may refer you to a counselor or therapist to help you find a solution.

Drowsiness that’s a side effect of medication is often curable. Your doctor may swap the medication for a different type or change your dosage until the drowsiness subsides. Never change your dosage or stop a medication without first talking to your doctor.

If no cause for your drowsiness is apparent, you may need to undergo some tests. These are usually noninvasive and painless. Your doctor could request a full blood count, urine tests, an electroencephalogram (EEG), or a computerized tomography (CT) scan.

If your doctor suspects that you may have sleep apnea, restless leg syndrome, or another sleep disorder, they may schedule a sleep study test. For this test, you’ll spend the night in the hospital or a sleep center under the observation and care of a sleep specialist. Your blood pressure, heart rate, breathing, and brain waves will be monitored throughout the night for any signs of a sleep disorder.

When to Seek Emergency Care 

You should seek medical attention if you begin to feel drowsy after you:

  • start a new medication
  • take an overdose of medication
  • sustain a head injury
  • become exposed to the cold

How Can Drowsiness Be Prevented?

Often, a regular amount of sleep each night can prevent drowsiness. Most adults require about eight hours of sleep to feel fully refreshed. Some people may need more, especially those with medical conditions or a particularly active lifestyle.

Talk to your doctor as soon as possible if you experience any changes in your mood, signs of depression, or uncontrollable feelings of stress and anxiety.

What Is the Outlook for Untreated Drowsiness?

You may find that drowsiness goes away naturally as your body becomes used to a new schedule or as you become less stressed, depressed, or anxious.

However, if the drowsiness is due to a medical problem or sleep disorder, it’s unlikely to get better on its own. In fact, the drowsiness is likely to worsen without proper treatment. Some people manage to live with drowsiness. However, it may limit your ability to work, drive, and operate machinery safely.

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See a list of possible causes in order from the most common to the least.


Head Injury

This condition is considered a medical emergency. Urgent care may be required.

A head injury could be an injury to the brain, skull, or scalp. It can vary in severity depending on the cause. In some cases face swelling can be a sign of a head injury.

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Stroke Overview

This condition is considered a medical emergency. Urgent care may be required.

A stroke (a "brain attack") is a medical emergency in which part of the brain is deprived of oxygen. This occurs when an artery that supplies oxygenated blood to the brain becomes damaged and brain cells begin to die.

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This condition is considered a medical emergency. Urgent care may be required.

Delirium is an abrupt change in the brain that causes mental confusion and emotional disruption. It makes it difficult to think, remember, sleep, pay attention, and more. You might experience the condition durin...

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This condition is considered a medical emergency. Urgent care may be required.

A concussion is a mild traumatic brain injury. Usually it occurs after an impact to your head or after a whiplash-type injury. A concussion can cause many severe symptoms that affect brain function.

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Hypovolemic Shock

This condition is considered a medical emergency. Urgent care may be required.

Hypovolemic shock (hemorrhagic shock) is a life-threatening condition that results when you lose more than 20 percent of your body's blood or fluid supply, preventing the heart from pumping sufficient blood to your body.

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Cardiogenic Shock

This condition is considered a medical emergency. Urgent care may be required.

Cardiogenic shock is a rare condition in which the heart is so damaged that it is unable to supply sufficient blood to bodily organs. Sweating and cold extremities are potential signs of this condition.

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This condition is considered a medical emergency. Urgent care may be required.

Meningitis is an inflammation of the membrane that covers the brain and spinal cord. It may cause headache and fever in teens and adults, irritability in babies, and trouble breathing in young children.

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This condition is considered a medical emergency. Urgent care may be required.

Encephalitis is an inflammation of the brain tissue. It's most often caused by viral infections. In some cases, bacterial infections can cause encephalitis.

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The Catastrophy of Cardiac Tamponade

This condition is considered a medical emergency. Urgent care may be required.

Cardiac tamponade is a very serious condition in which your heart can't pump enough blood to your body due to fluid buildup around your heart.

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Low Blood Sodium (Hyponatremia)

Low blood sodium, or hyponatremia, occurs when water and sodium are out of balance in your body. A quick drop in sodium levels can cause weakness, headache, nausea, and muscle cramps.

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Narcolepsy is a disorder of the nervous system. It causes drowsiness and sleep attacks. It's also known as daytime sleep disorder and cataplexy. The Center for Narcolepsy (CN) at Stanford University School of Medicin...

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Brain Tumor

A brain tumor is a collection or mass of abnormal cells in your brain. A brain tumor can be cancerous (malignant) or non-cancerous (benign).

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Sleep Disorders

Sleep disorders/disturbances can cause your sleep to be disturbed. Disturbed sleep includes the inability to fall asleep, the inability to go back to sleep, and frequent waking up during the night. Sleep disorders ca...

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Migraine with Aura

Migraine is a disorder characterized by repeated attacks of severe headache. Symptoms include throbbing or pulsating pain, usually on only one side of the head, and can last between four hours and three days.

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Hypercalcemia is a condition in which you have too much calcium in your blood. Serious cases could cause symptoms like abdominal pain, nausea, constipation, and weakness.

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Acute Mountain Sickness

Acute mountain sickness (altitude sickness or high altitude pulmonary edema) occurs in high altitudes, especially when exercising. A lack of oxygen can give the skin and lips a blue tinge.

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The thyroid gland produces a hormone that controls how your cells use energy (metabolize). Hypothyroidism occurs when the body doesn't produce enough. Untreated, it can cause complications like obesity and heart disease.

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Nicotine Dependence

Nicotine addiction occurs when a person becomes addicted to nicotine, which is a chemical found in tobacco. The addiction is physical, mental, and behavioral.

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Mini Stroke (Transient Ischemic Attack)

This condition is considered a medical emergency. Urgent care may be required.

During a transient ischemic attack (TIA, mini stroke) blood stops flowing to the brain for a short period of time. TIA doesn't kill brain cells like a stroke does. TIA causes symptoms that mimic those of a stroke.

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Epidural Hematoma

This condition is considered a medical emergency. Urgent care may be required.

An epidural hematoma occurs when blood fills the area between the skull and the protective covering of the brain. It usually results from a traumatic injury to the head, and puts you at risk for brain damage or death.

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This feature is for informational purposes only and should not be used to diagnose.
Please consult a healthcare professional if you have health concerns.