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Daytime Sleepiness – Finding the Cause

Do you feel tired all the time no matter

how much sleep you get?

Daytime sleepiness has a significant impact on quality of life. People with daytime sleepiness struggle with social, academic and work demands,they are at risk of motor vehicle and workplace

accidents and generally have poorer health than comparable adults.

Accurate diagnosis is important, not only because of the negative impacts of sleepiness and its root causes on health

and social function but because excessive sleepiness is generally remediable with appropriate treatment [1]. The list of possible causes of excessive daytime sleepiness spans virtually every major area of medicine, neurology and psychiatry. A clear, detailed history is invaluable in negotiating these numerous diagnostic considerations [2].

To assist patients and doctors when considering the cause of daytime sleepiness we have compiled a list of known causes and routine tests. Please note: there are numerous possible causes, this is by no means a complete list. It is only intended as a guide to assist you and your doctor find the cause of your excessive daytime sleepiness.


Behavioural sleep deprivation The most common cause of daytime sleepiness is insufficient sleep/poor sleep hygiene. Sleep-related breathing disorders

Sleep apnea. Residual sleepiness in treated obstructive sleep apnea. Upper Airway Resistance Syndrome.

Other sleep disorders

Includes circadian rhythm sleep disorders (Delayed Sleep Phase Syndrome, shift work disorder), REM Sleep Behaviour Disorder and other Parasomnias, Post-traumatic hypersomnia (following head trauma or illness) Insomnia, Narcolepsy. Also sleep-related movement disorders (Periodic Limb Movement Disorder, Restless Legs Syndrome).


Mental health conditions Including Depression, Anxiety, Bipolar Disorder.


Includes prescription, non-prescription, and drugs of abuse. *refer to list of medications below.


Including head trauma, stroke, cancer, inflammatory conditions, encephalitis, neurodegenerative conditions (eg: Parkinson Disease, myotonic dystrophy etc), Chronic Fatigue Syndrome, Fibromyalgia, Hypothyroidism (Hashimotos), Ehlers-Danlos Syndrome, Arnold-Chiari Malformation, Multiple Sclerosis. Other medical conditions that are associated with sleep fragmentation can result in daytime sleepiness, including: arthritis, spondylosis, chronic pain of any nature, nocturnal angina, epilepsy, asthma, chronic obstructive pulmonary disease, alcoholism, urinary dysfunction and gastrointestinal disorders (e.g. peptic ulcer disease), gastro-oesophageal refux and irritable bowel syndrome


Hypersomnia that develops after a viral infection including mononucleosis (glandular fever/mono), or Guillain-Barre syndrome. Patients may experience fatigue and hypersomnolence and can sleep most of the 24-hour day. The outcome tends to be favourable; however, the resolution may take months or even years [3].

Long sleepers, also called "healthy hypersomniacs," are people who require more sleep at night than normal. They may be misdiagnosed with idiopathic hypersomnia because of extremely long sleep episodes at night. These subjects are normally alert, however, once they have obtained their required amount of sleep [4].

Medication Classes Commonly Associated with Daytime Sleepiness

  • Alpha-adrenergic blocking agents

  • Anticonvulsants (e.g., hydantoins, succinimides)

  • Antidepressants (monoamine oxidase inhibitors, tricyclics, selective serotonin reuptake inhibitors)

  • Antidiarrhea agents

  • Antiemetics

  • Antihistamines

  • Antimuscarinics and antispasmodics

  • Antiparkinsonian agents

  • Antipsychotics

  • Antitussives

  • Barbiturates

  • Benzodiazepines, other γ-aminobutyric acid affecting agents, and other anxiolytics

  • Beta-adrenergic blocking agents

  • Genitourinary smooth muscle relaxants

  • Opiate agonists and partial opiate agonists

  • Skeletal muscle relaxants

Routine tests to consider for causes of daytime sleepiness

  • Thyroid tests should include: TSH, Free T3 (FT3), Free T4 (FT4), Reverse T3 (rT3), and thyroid antibodies for Hashimoto's Thyroiditis

  • Nutrient deficiencies including vitamin D (25-Hydroxy), B12 and serum folate, magnesium, zinc, iodine and selenium

  • Iron studies: Iron, TIBC, %Sat, Ferritin

  • Carnitine panel: free, total, esterified, esterified/free

  • C-Reactive Protein

  • Complete Blood Count

  • Complete Metabolic Panel (glucose, sodium, creatinine, etc)

  • Cortisol (preferably 8 am spot cortisol or 24-hr urinary cortisol)

Excessive daytime sleepiness affects at least 20% of the population and identifying the underlying cause can often prove difficult. While it may be tempting for a doctor to diagnose Idiopathic Hypersomnia in cases of excessive daytime sleepiness of unknown cause this does a gross disservice to the many patients that in fact do not meet the clinical definition of Idiopathic Hypersomnia.

Idiopathic Hypersomnia is a neurological disorder diagnosed by identifying key clinical features and by a thorough exclusion process. Unfortunately, a lack of awareness and proper understanding of what these key clinical features are and a less than thorough exclusion process can result in misdiagnosis and unnecessary prescription of stimulant medications. It can also result in the underlying cause remaining unidentified and untreated.

"Idiopathic hypersomnia is probably one of the most frequently overdiagnosed sleep disorders because there is a tendency to classify in this category all hypersomnias that do not fit the criteria of either narcolepsy or the sleep apnea syndrome. Indeed, the difficulty does not stem from disorders of excessive daytime sleepiness, such as narcolepsy or the obstructive sleep apnea syndrome, which are identified easily by their clinical and polysomnographic features; instead, it comes from other disorders associated with excessive daytime sleepiness that require more sophisticated investigation or that still are delineated insufficiently both clinically and polysomnographically.”– Professor Michel Billiard 5

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1, 2. 3, 4, 5. First published on Hypersomnolence Australia's website in July 2015

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