Causes of Excessive Daytime Sleepiness
The causes of excessive daytime sleepiness can be broadly grouped into lifestyle-related factors, sleep disorders, and medical conditions. Excessive daytime sleepiness is usually a sign that the brain is not getting enough high-quality sleep or is being affected by disrupted sleep cycles or chronic fatigue.
Lifestyle and Behavioural Causes
Poor sleep habits are a leading contributor:
Inadequate sleep duration, often due to late nights, shift work, or busy schedules
Irregular sleep patterns, especially among students or travellers
Excessive screen time before bed, which suppresses melatonin production
Stimulant or alcohol use, which disrupts deep sleep stages
Poor diet and lack of exercise, both of which reduce sleep quality
Sleep Disorders
Several sleep-related conditions directly result in daytime sleepiness:
Obstructive sleep apnoea (OSA) – A common condition where the airway collapses during sleep, causing repeated wake-ups and reduced oxygen supply
Narcolepsy – A neurological disorder where the brain cannot regulate sleep-wake cycles properly, leading to sudden sleep attacks
Restless legs syndrome (RLS) – Causes uncontrollable urges to move the legs, disturbing sleep
Insomnia – Difficulty falling or staying asleep, often linked to anxiety or depression
Delayed sleep phase disorder – A circadian rhythm condition where the body’s internal clock is shifted later than normal
Medical Conditions
Some underlying health problems cause fatigue and reduced alertness:
Depression and anxiety – Common mental health conditions that alter sleep patterns
Chronic fatigue syndrome – Characterised by persistent exhaustion unrelieved by rest
Anaemia – Reduced oxygen-carrying capacity in the blood can lead to tiredness
Thyroid disorders, especially hypothyroidism
Diabetes, particularly if poorly controlled
Medication side effects, including sedatives, antihistamines, or antidepressants
Causes of Excessive Daytime Sleepiness In South Africa
In South Africa, undiagnosed sleep apnoea is a significant contributor, especially among people with obesity or hypertension. Many patients are unaware of the condition and may be misdiagnosed with depression or burnout. Limited access to sleep studies in public hospitals adds to the underdiagnosis.
Understanding the causes of excessive daytime sleepiness helps patients and healthcare providers pinpoint the issue and begin proper treatment—whether that means improving sleep hygiene, treating a sleep disorder, or managing a medical condition.
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