Why Am I So Tired? Common Causes of Excessive Daytime Sleepiness

Excessive Daytime Sleepiness (EDS) is more than feeling a bit tired after a late night. It’s a persistent, often overwhelming drowsiness that interferes with daily functioning—struggling to stay awake in meetings, fighting heavy eyelids while driving, or nodding off during conversations. If this describes your experience, you’re not alone: studies suggest 10-20% of adults experience significant daytime sleepiness.

EDS is a symptom, not a diagnosis. It signals that something is wrong with your sleep—either you’re not getting enough, the quality is poor, or an underlying condition is disrupting your body’s ability to maintain wakefulness. Identifying the cause is the first step toward feeling alert again.

A high score on the Epworth Sleepiness Scale (ESS) is a strong indicator of EDS. But what’s causing it? The possibilities range from simple lifestyle factors to serious medical conditions.

How to Know If You Have EDS

Normal tiredness after a poor night’s sleep is different from EDS. Signs that suggest true excessive sleepiness include:

• Difficulty staying awake during passive activities (watching TV, reading, attending meetings)
• Falling asleep unintentionally (microsleeps)
• Needing caffeine just to function at a basic level
• Feeling unrefreshed despite sleeping 7-8 hours
• Difficulty concentrating or “brain fog”
• Irritability and mood changes
• Reduced motivation and productivity

The Epworth Sleepiness Scale provides an objective measure. It asks you to rate your likelihood of dozing off in eight common situations. A score above 10 suggests excessive sleepiness; above 16 indicates severe sleepiness that warrants medical evaluation.

Cause #1: Insufficient Sleep

The most common cause of daytime sleepiness is also the most obvious: not sleeping enough. Yet many people underestimate how much sleep they need or overestimate how much they’re getting.

How Much Sleep Do You Actually Need?

Most adults need 7-9 hours of sleep per night. This isn’t a suggestion—it’s a biological requirement. The idea that some people can thrive on 5-6 hours is largely a myth. While rare genetic variants allow a small percentage of people to function on less sleep, most who claim to need little sleep are simply accustomed to chronic sleep deprivation.

The Sleep Debt Problem

Sleep debt accumulates. If you need 8 hours but consistently get 6, you’re building a deficit of 14 hours per week. This debt doesn’t disappear—it accumulates and manifests as increasing sleepiness, cognitive impairment, and health problems.

A single night of recovery sleep doesn’t erase accumulated debt. Research suggests it can take several nights of extended sleep to fully recover from chronic sleep restriction.

Why People Don’t Sleep Enough

Voluntary sleep restriction: Work demands, social activities, screen time, and the belief that sleep is negotiable lead many people to chronically shortchange their sleep.

Sleep opportunity vs. sleep time: Being in bed for 8 hours doesn’t mean sleeping for 8 hours. If it takes you 30 minutes to fall asleep and you wake for 30 minutes during the night, your actual sleep time is 7 hours.

Unrecognized sleep disorders: Conditions like sleep apnea can fragment sleep without your awareness, leaving you sleep-deprived despite adequate time in bed.

The Solution

Track your sleep honestly for two weeks. Note when you get into bed, when you fall asleep (estimate), when you wake, and when you get up. Calculate your actual sleep time. If it’s consistently below 7 hours, the solution is straightforward: prioritize more sleep.

Cause #2: Poor Sleep Quality

Sometimes the problem isn’t sleep quantity but quality. You can spend 8 hours in bed and still wake unrefreshed if your sleep is fragmented or you’re not cycling through the restorative stages properly.

What Disrupts Sleep Quality?

Environmental factors:

• Noise (traffic, snoring partner, pets)
• Light (streetlights, electronics, early sunrise)
• Temperature (too hot is worse than too cold)
• Uncomfortable mattress or pillow

Behavioral factors:

• Alcohol before bed (causes fragmented sleep in the second half of the night)
• Caffeine too late in the day
• Irregular sleep schedule
• Screen use before bed
• Eating large meals late

Medical factors:

• Pain (arthritis, back problems)
• Frequent urination (nocturia)
• Medications that disrupt sleep
• Undiagnosed sleep disorders

Assessing Your Sleep Quality

The Pittsburgh Sleep Quality Index (PSQI) evaluates multiple dimensions of sleep quality, including:

• Subjective sleep quality
• Sleep latency (time to fall asleep)
• Sleep duration
• Sleep efficiency (time asleep vs. time in bed)
• Sleep disturbances
• Use of sleep medication
• Daytime dysfunction

A PSQI score above 5 indicates poor sleep quality.

The Solution

Optimize your sleep environment and habits. Keep your bedroom cool (65-68°F/18-20°C), dark, and quiet. Maintain a consistent sleep schedule. Limit alcohol and caffeine. If problems persist despite good sleep hygiene, consider whether an underlying condition might be responsible.

Cause #3: Obstructive Sleep Apnea (OSA)

OSA is one of the most common—and most underdiagnosed—causes of excessive daytime sleepiness. An estimated 80% of moderate-to-severe cases remain undiagnosed.

What Is OSA?

During sleep, the muscles supporting the soft tissues in your throat relax. In people with OSA, this relaxation causes the airway to narrow or completely collapse, stopping breathing for 10 seconds to over a minute. The brain detects the oxygen drop and briefly arouses you to restore breathing—often with a gasp or snort.

These arousals are usually too brief to remember, but they fragment sleep and prevent you from reaching the deep, restorative stages. People with severe OSA may experience 30-100+ breathing interruptions per hour, meaning they never get consolidated sleep despite spending adequate time in bed.

Signs of OSA

• Loud, chronic snoring (often reported by bed partner)
• Witnessed breathing pauses during sleep
• Gasping or choking during sleep
• Waking with a dry mouth or sore throat
• Morning headaches
• Excessive daytime sleepiness despite adequate sleep time
• Difficulty concentrating
• Irritability

Risk Factors

• Obesity (the strongest risk factor)
• Male sex (though women’s risk increases after menopause)
• Age over 40
• Large neck circumference (>17 inches in men, >16 inches in women)
• Family history of OSA
• Anatomical factors (large tonsils, recessed chin, deviated septum)

The Solution

If you suspect OSA, take our OSA Risk Assessment Quiz and discuss your symptoms with a doctor. Diagnosis requires a sleep study (polysomnography), which can often be done at home. Treatment—usually CPAP therapy—is highly effective and can dramatically improve daytime alertness.

Cause #4: Other Sleep Disorders

Beyond OSA, several other sleep disorders cause excessive daytime sleepiness.

Narcolepsy

Narcolepsy is a neurological disorder affecting the brain’s ability to regulate sleep-wake cycles. It’s characterized by:

• Overwhelming daytime sleepiness regardless of nighttime sleep
• Sudden “sleep attacks”—falling asleep without warning
• Cataplexy (in Type 1 narcolepsy)—sudden muscle weakness triggered by strong emotions
• Sleep paralysis—inability to move when falling asleep or waking
• Hypnagogic hallucinations—vivid, dream-like experiences at sleep onset

Narcolepsy affects about 1 in 2,000 people but is often misdiagnosed as depression, epilepsy, or simply “laziness.” It typically begins in adolescence or young adulthood.

Idiopathic Hypersomnia

Similar to narcolepsy but without cataplexy or the characteristic REM sleep abnormalities. People with idiopathic hypersomnia sleep excessively (often 10+ hours) yet still feel unrefreshed and struggle with severe daytime sleepiness. The cause is unknown.

Restless Legs Syndrome (RLS)

RLS causes uncomfortable sensations in the legs (described as crawling, tingling, or aching) and an irresistible urge to move them. Symptoms are worst in the evening and during rest, making it difficult to fall asleep. The resulting sleep deprivation causes daytime sleepiness.

Periodic Limb Movement Disorder (PLMD)

PLMD involves repetitive, involuntary leg movements during sleep—typically every 20-40 seconds. These movements cause brief arousals that fragment sleep, leading to daytime sleepiness. Unlike RLS, people with PLMD are usually unaware of the movements.

Circadian Rhythm Disorders

Your internal clock may be misaligned with your schedule:

Delayed Sleep Phase Disorder: Your natural sleep time is significantly later than conventional schedules require. Common in adolescents and young adults. You can’t fall asleep until 2-3 AM but then sleep normally—the problem is the timing, not the sleep itself.

Advanced Sleep Phase Disorder: The opposite—you get sleepy very early (6-8 PM) and wake very early (3-5 AM). More common in older adults.

Shift Work Disorder: Working nights or rotating shifts forces you to sleep when your body wants to be awake and work when it wants to sleep.

Cause #5: Medical Conditions

Many medical conditions cause fatigue or sleepiness as a symptom.

Conditions That Cause Sleepiness

Hypothyroidism: An underactive thyroid slows metabolism and causes fatigue, weight gain, and sleepiness. A simple blood test can diagnose it.

Anemia: Reduced oxygen-carrying capacity of the blood causes fatigue and can contribute to sleepiness. Iron deficiency is the most common cause.

Depression: Fatigue and sleep disturbances (either insomnia or hypersomnia) are core symptoms of depression. The relationship is bidirectional—poor sleep worsens depression, and depression disrupts sleep.

Chronic fatigue syndrome: Characterized by profound fatigue that doesn’t improve with rest and worsens with physical or mental exertion.

Heart failure: The heart’s reduced pumping capacity leads to fatigue and can cause sleep-disordered breathing.

Kidney disease: Accumulation of waste products causes fatigue and disrupts sleep.

Diabetes: Both high and low blood sugar can cause fatigue. Diabetes also increases OSA risk.

Medications That Cause Sleepiness

Many medications list drowsiness as a side effect:

• Antihistamines (especially first-generation like diphenhydramine)
• Benzodiazepines and sleep medications
• Some antidepressants
• Opioid pain medications
• Some blood pressure medications
• Anti-seizure medications
• Muscle relaxants

If you started a new medication around the time your sleepiness began, discuss alternatives with your doctor.

Cause #6: Lifestyle Factors

Sometimes the cause is simpler than a medical condition.

Caffeine Patterns

Caffeine blocks adenosine receptors, masking sleepiness. But it has a half-life of 5-6 hours, meaning half the caffeine from your 3 PM coffee is still in your system at 9 PM. This can:

• Delay sleep onset
• Reduce deep sleep
• Create a cycle of poor sleep → more caffeine → poorer sleep

Alcohol

Alcohol is sedating but severely disrupts sleep architecture. It suppresses REM sleep in the first half of the night and causes fragmented sleep in the second half as it’s metabolized. Regular evening drinking can cause chronic sleep deprivation.

Irregular Schedule

Varying your sleep and wake times—sleeping in on weekends, staying up late some nights—confuses your circadian rhythm. This “social jet lag” impairs sleep quality and causes daytime sleepiness.

Physical Inactivity

Regular exercise improves sleep quality and daytime alertness. Sedentary lifestyles are associated with poorer sleep and more daytime fatigue.

What to Do Next

Step 1: Quantify Your Sleepiness

Take the Epworth Sleepiness Scale (ESS). This gives you an objective measure to track and to share with your doctor.

Step 2: Evaluate Your Sleep

• Are you getting 7-9 hours of actual sleep?
• Is your sleep quality good? Take the PSQI.
• Do you have symptoms of sleep apnea? Take the OSA Risk Assessment.

Step 3: Address Lifestyle Factors

• Establish a consistent sleep schedule
• Optimize your sleep environment
• Limit caffeine after noon
• Reduce alcohol, especially before bed
• Increase physical activity

Step 4: Seek Medical Evaluation If Needed

See a doctor if:

• Your ESS score is above 10
• You have symptoms of sleep apnea
• Sleepiness persists despite adequate sleep and good sleep hygiene
• Sleepiness is severe enough to affect safety (driving, work)
• You have other concerning symptoms

The Bottom Line

Excessive daytime sleepiness is not normal and shouldn’t be accepted as inevitable. It’s a signal that something is wrong—whether that’s simply not prioritizing sleep, a treatable sleep disorder, or an underlying medical condition.

The first step is honest assessment: How much are you actually sleeping? What’s your sleep quality like? Do you have risk factors for sleep disorders? From there, you can address lifestyle factors, seek appropriate testing, and get treatment if needed.

Feeling alert and energetic during the day is achievable. It starts with taking your sleepiness seriously.