Excessive daytime sleepiness: what are the most common medical causes?

Excessive daytime sleepiness (EDS)—the persistent sense of drowsiness or an urgent need to nap during the day—can have many underlying medical causes. It affects work performance, driving safety and overall quality of life. Understanding the most common medical reasons for EDS can help you and your doctor find the right diagnosis and treatment.

Measuring Daytime Sleepiness
The Epworth Sleepiness Scale (Johns MW, 1991) is a simple questionnaire that asks how likely you are to doze off in eight everyday situations (e.g., sitting and reading, watching TV). Scores range from 0 to 24. A score above 10 suggests significant daytime sleepiness and may warrant further evaluation by a sleep specialist.

1. Sleep Disorders
   Sleep disorders are among the leading medical causes of EDS. Common conditions include:

• Obstructive Sleep Apnea (OSA)
  • Airways collapse during sleep, causing brief breathing pauses.
  • Fragmented sleep leads to unrefreshing rest and daytime drowsiness.
  • Often associated with loud snoring, gasping or choking at night.

• Narcolepsy
  • A neurological disorder characterized by overwhelming daytime sleep attacks.
  • May include cataplexy (sudden muscle weakness) triggered by strong emotion.
  • Typically starts in adolescence or early adulthood.

• Restless Legs Syndrome (RLS) and Periodic Limb Movement Disorder (PLMD)
  • Urge to move legs or involuntary leg jerks disrupt sleep continuity.
  • Often worse at night or when lying down, leading to nonrestorative sleep.

• Insomnia
  • Difficulty falling asleep, staying asleep or waking too early.
  • Chronic insomnia can reduce total sleep time and impair daytime alertness.

2. Inadequate Sleep Duration or Poor Sleep Habits
   Not getting enough sleep—whether due to lifestyle, work schedules or poor sleep hygiene—can directly cause EDS. Common contributors:

• Shift work or rotating shifts
• Irregular bedtimes and wake times
• Excessive screen time before bed (blue light exposure)
• Caffeine, alcohol or heavy meals close to bedtime

3. Circadian Rhythm Disorders
   Your body’s internal clock regulates sleep–wake cycles. When this clock is out of sync, you can experience EDS:

• Delayed Sleep Phase Syndrome (night owl pattern)
• Advanced Sleep Phase Syndrome (early evening sleepiness)
• Jet lag and shift-work disorder

4. Medications and Substances
   Many prescription and over-the-counter drugs list drowsiness as a side effect. Examples include:

• Antihistamines (e.g., diphenhydramine)
• Opioid pain relievers
• Antidepressants and antipsychotics
• Anti-seizure medications
• Muscle relaxants
• Alcohol and sedatives (e.g., benzodiazepines)

If you suspect a medication is making you sleepy, do not stop it suddenly—talk to your prescribing provider first.

5. Mental Health Conditions
   Depression, anxiety and other mood disorders commonly overlap with sleep problems:

• Depression can cause early-morning awakening and nonrestorative sleep.
• Anxiety may lead to racing thoughts at night, fragmented sleep and daytime fatigue.
• Post-traumatic stress disorder (PTSD) often involves nightmares and hyperarousal.

6. Medical and Neurological Disorders
   Chronic illnesses can disrupt sleep quality or the brain’s arousal systems:

• Hypothyroidism
  • Low thyroid hormone slows metabolism.
  • Symptoms include fatigue, weight gain and cold intolerance.

• Anemia
  • Low red blood cell count reduces oxygen delivery to tissues.
  • Common in iron-deficiency, chronic disease and blood loss.

• Chronic Kidney Disease
  • Uremia can cause poor sleep and restless legs.
  • Dialysis schedules may disrupt normal sleep patterns.

• Chronic Liver Disease and Hepatic Encephalopathy
  • Accumulation of toxins (e.g., ammonia) can impair brain function.
  • May present as confusion, sleep–wake reversal and lethargy (Kamath & Wiesner, 2001; EASL 2018 guidelines).

• Neurological Conditions
  • Parkinson’s disease, multiple sclerosis and traumatic brain injury can impair sleep architecture.
  • Neurodegenerative processes may directly affect wake-promoting brain regions.

7. Metabolic and Endocrine Disorders
   Problems with blood sugar or hormonal imbalances can trigger EDS:

• Diabetes Mellitus
  • Fluctuating blood sugar levels may cause fatigue and poor sleep.
  • Peripheral neuropathy and nocturia (nighttime urination) fragment sleep.

• Adrenal Insufficiency
  • Low cortisol levels lead to weakness, low blood pressure and sleep disturbances.

8. Cardiovascular and Respiratory Disorders
   Heart and lung diseases can compromise nighttime breathing or oxygenation:

• Chronic Obstructive Pulmonary Disease (COPD)
  • Nighttime hypoxia may lead to unrefreshing sleep.
  • Co-existing sleep apnea is common.

• Congestive Heart Failure
  • Fluid buildup and paroxysmal nocturnal dyspnea (PND) wake you from sleep.
  • Sleep fragmentation worsens daytime fatigue.

When to Seek Help
If excessive daytime sleepiness persists despite improving sleep habits, or if you experience any of the following, speak to a doctor promptly:

• Loud, chronic snoring with gasping episodes
• Sudden muscle weakness or paralysis with strong emotions
• Involuntary leg movements at night
• Unexplained weight gain or loss, cold intolerance
• Symptoms of depression or anxiety affecting daily life
• Chest pain, shortness of breath, or swelling in legs

You might consider doing a free, online symptom check for excessive daytime sleepiness to help identify potential causes and guide your next steps.

Diagnosis and Next Steps
Your healthcare provider may recommend:

• Detailed sleep history and sleep diary
• Epworth Sleepiness Scale or other questionnaires
• Polysomnography (sleep study) to assess breathing, limb movements and sleep stages
• Actigraphy (wrist-watch-like device) to track sleep–wake patterns
• Blood tests to screen for anemia, thyroid function, kidney and liver health
• Neurological evaluation if narcolepsy or other central disorders are suspected

Treatment
Managing EDS depends on the underlying cause:

• Sleep Apnea: Continuous positive airway pressure (CPAP), oral appliances, lifestyle changes
• Narcolepsy: Medications (e.g., modafinil, sodium oxybate), scheduled naps, good sleep hygiene
• Insomnia: Cognitive behavioral therapy for insomnia (CBT-I), sleep hygiene measures, short-term medications
• RLS/PLMD: Iron supplementation, dopamine agonists, anticonvulsants
• Medical Conditions: Treat thyroid disorders, anemia, diabetes, kidney or liver disease as appropriate
• Lifestyle Adjustments: Regular sleep schedule, limiting caffeine/alcohol, stress-reduction techniques

Final Thoughts
Excessive daytime sleepiness is a common but treatable symptom. Identifying the root cause is key to restoring alertness and improving your quality of life. Don’t ignore persistent drowsiness—talk to your doctor about any concerning symptoms, especially those that could signal a serious or life-threatening condition. A thorough evaluation, including a sleep study or targeted blood tests, can set you on the path to feeling more rested and energetic each day.