Drowsiness: Why You Feel Sleepy and When to Worry

What drowsiness is

Drowsiness (somnolence) is a strong pull toward sleep: heavy eyelids, yawning, slower thinking and nodding off. It is different from fatigue, which is low energy or exhaustion without necessarily wanting to sleep. Many people have both, but separating them helps find the cause. For a related overview, see sleepiness.

Doctors often measure drowsiness with the Epworth Sleepiness Scale, which asks how likely you are to doze in 8 everyday situations, such as reading or as a passenger in a car. A score above 10 out of 24 suggests excessive daytime sleepiness.

Common causes of drowsiness

Not enough sleep

Adults need 7 to 9 hours of sleep a night, teenagers 8 to 10. Many people regularly get less and build up a "sleep debt" that causes daytime drowsiness, poorer concentration and slower reactions. Teens are especially affected because their body clocks shift later while school starts early.

Poor-quality sleep

• Obstructive sleep apnea: the throat repeatedly closes during sleep, cutting off breathing for seconds at a time. Loud snoring, gasping, morning headaches and daytime drowsiness despite a full night in bed are typical. It is common in people with obesity, a thick neck or large tonsils, but can affect anyone.
• Restless legs syndrome: an urge to move the legs in the evening that delays sleep.
• Insomnia, pain, frequent urination at night, reflux and a noisy or bright bedroom all fragment sleep.

Shift work and body clock problems

Night shifts, rotating shifts and jet lag put sleep out of step with the body clock. Delayed sleep phase, common in teens, makes it hard to fall asleep before 1 or 2 a.m. and hard to wake. See circadian rhythm disorders.

Medicines and substances

• sedating antihistamines (diphenhydramine, chlorpheniramine), including in nighttime cold medicines
• sleeping pills, benzodiazepines, some antidepressants and antipsychotics
• opioids, gabapentin, pregabalin and muscle relaxants
• some blood pressure medicines and anti-seizure drugs
• alcohol and cannabis, and withdrawal from caffeine or stimulants

Medical conditions

• Hypothyroidism: tiredness, weight gain, feeling cold, constipation and dry skin.
• Anemia: tiredness, breathlessness and pale skin.
• Depression: can cause sleeping too much, with low mood and loss of interest.
• Diabetes: high or low blood sugar causes drowsiness.
• Kidney and liver disease: toxins build up and cause sleepiness.
• Infections: flu, COVID-19, mononucleosis and others; drowsiness can linger for weeks.
• Heart failure, COPD and other chronic illnesses.

Sleep disorders of the brain

• Narcolepsy: overwhelming daytime sleepiness and sudden sleep attacks, sometimes with cataplexy (brief muscle weakness triggered by laughter or surprise), vivid dreams on falling asleep, and sleep paralysis. It usually starts in the teens or twenties.
• Idiopathic hypersomnia: long nights of sleep, very hard waking ("sleep drunkenness") and unrefreshing naps.

Sudden drowsiness: emergency causes

New, sudden or rapidly worsening drowsiness needs urgent assessment because it may mean the brain is not working properly:

• head injury and bleeding in or around the brain
• stroke
• poisoning or overdose, including alcohol, opioids and sedatives
• carbon monoxide poisoning, from faulty heaters, generators or car exhaust
• very low or very high blood sugar
• meningitis, encephalitis and sepsis
• severe dehydration, low sodium or kidney failure

Drowsiness after eating

A mild dip in alertness after a large meal, especially at lunchtime, is normal. It reflects the natural afternoon dip in the body clock plus digestion. Large meals high in refined carbohydrates and alcohol make it worse. Marked sleepiness after meals with thirst, frequent urination or weight loss can be a sign of diabetes.

How doctors find the cause

A doctor will ask how much you sleep, your sleep schedule, snoring, medicines, alcohol, mood and other symptoms. A sleep diary for 2 weeks and a bed partner's description of your night help. Tests may include:

• blood tests: blood count, thyroid function, glucose and HbA1c, kidney and liver function, vitamin B12, iron
• home sleep apnea test or overnight polysomnography in a sleep lab
• multiple sleep latency test: a series of daytime naps to diagnose narcolepsy and idiopathic hypersomnia
• depression screening questionnaires

Treatment and what helps

Improve sleep

• Aim for 7 to 9 hours in bed, at a regular time, including weekends.
• Keep the bedroom dark, cool and quiet; put screens away 1 hour before bed.
• Avoid caffeine after early afternoon and alcohol near bedtime.
• Get daylight in the morning and stay active during the day.
• A short nap of 10 to 20 minutes before 3 p.m. can restore alertness without harming night sleep.

Treat the cause

• Sleep apnea: CPAP is highly effective; other options include mouthpieces, weight loss and, for some, surgery or newer medicines.
• Medicines: your doctor may switch to a non-sedating alternative or change the timing. Do not stop prescription medicines on your own.
• Thyroid, anemia, diabetes and depression: treatment usually lifts drowsiness.
• Narcolepsy and idiopathic hypersomnia: scheduled naps and wake-promoting medicines prescribed by a sleep specialist.

Frequently asked questions

What causes drowsiness during the day?

The commonest causes are not enough sleep, sleep apnea, shift work, sedating medicines and alcohol. Depression, hypothyroidism, anemia, diabetes, and sleep disorders such as narcolepsy are other causes. A doctor can test for these if good sleep habits do not fix it.

What is the difference between drowsiness and fatigue?

Drowsiness is an urge to fall asleep. Fatigue is a lack of energy or exhaustion that may not make you want to sleep, and rest may not relieve it. Sleep disorders mostly cause drowsiness, while depression, anemia and chronic illness often cause both.

When is drowsiness a medical emergency?

Drowsiness is an emergency when it comes on suddenly, the person is hard to wake, or it comes with confusion, slurred speech, one-sided weakness, a severe headache, a head injury, a possible overdose or poisoning, or slow breathing. Call 911.

Why am I drowsy even after 8 hours of sleep?

Poor-quality sleep is the usual reason, most often from sleep apnea, restless legs or frequent waking. Medicines, alcohol, depression, thyroid problems, anemia and narcolepsy can also cause it. Persistent drowsiness despite enough sleep deserves a doctor's assessment and possibly a sleep study.

Which medicines cause drowsiness?

Sedating antihistamines, sleeping pills, benzodiazepines, opioids, some antidepressants and antipsychotics, gabapentin, pregabalin, muscle relaxants and some anti-seizure and blood pressure medicines commonly cause drowsiness. Check the label and ask your pharmacist.