What is drowsiness?



Drowsiness is a state of sleepiness. By implication, this is abnormal when it is

  • Persistent,
  • Occurs at inappropriate times, or is
  • Excessive in nature.

Most often, drowsiness becomes a problem because it interferes with normal daytime activities.

Symptoms and consequences

Sleep deprivation or disturbance may result in excess daytime drowsiness, with serious consequences such as:

  • Quality of life may diminish as patients cut back on pleasure activities. Daytime naps become necessary, and can be embarrassing. At work, productivity decreases.
  • Mental changes: short-term memory is disturbed, attention span is shortened, energy levels and libido drop, the patient becomes irritable and shows poor judgment.
  • Patients become more accident-prone.
  • Breathing problems are frequent, such as sleep apnoea.
  • Immune function is decreased.
  • There are changes in appetite: sleep-deprived patients have an increased appetite for kilojoule-dense foods with high carbohydrate content.


The most common causes of drowsiness are

1. Medication side-effects
Drugs used for a variety of illnesses have ingredients which affect brain function in some way. Sedation is a known and frequent side-effect, often warned about on the drug’s label. Some common medications causing drowsiness are:

  • Cold medications,
  • Cough treatments,
  • Anti-depressants and anti-anxiety agents,
  • Anti-Parkinson’s treatment,
  • Alzheimer’s medication,
  • Some painkillers, and
  • Sleeping pills – they are meant to make you sleepy at night, but many have a “hangover” effect the next day.

2. Poor sleep quantity or quality
Many things can cause this problem, such as illness, anxiety states, work demands, or lifestyle choices. This is seldom a permanent state, and can be manipulated.
Sleep apnoea – probably the most common cause of disabling daytime sleepiness, is associated with obesity, and consists of episodes in which the patient stops breathing for a few moments during sleep. Sleep is thus disturbed, and is followed by excess daytime drowsiness.

3. Underlying medical conditions

  • Hypothyroidism and hyponatremia (low sodium in the blood) are the two best known causes.
  • Very low or very high blood sugar in poorly managed diabetics can cause drowsiness, even coma, and can be a medical emergency.
  • Organ failure – severe liver failure can cause drowsiness due to the brain being affected by accumulated toxins.
  • Obesity is associated with drowsiness and other sleep disorders.

4. Narcolepsy
This is a recognised sleep disorder, affecting 25 to 50 in every 100,000 people. If affects men and women equally, often begins in adolescence, may get worse at first, then persist for life. Cases are nearly always sporadic, and not familial. Some cases are secondary to tumours or strokes: these patients will have other neurologic signs as well, making the diagnosis obvious.

The normal elements of sleep and wakefulness cycles become muddled, so that patients may be sleepy by day, but cannot sleep at night. They often also have hypnagogic hallucinations, sleep paralysis, and a few have cataplexy: these are particular symptoms which identify narcolepsy from ordinary sleep disturbances. Narcoleptics have a shortage of orexin, a substance affecting brain function.


The patient’s complaint is easy to understand, but the extent may need to be measured. For this, special tests may be done, such as polysomnography and the multiple sleep latency (MSL) test. These are done at a sleep centre laboratory.

Underlying medical problems and disorders will be identified on examination, and appropriate tests will be done to confirm the diagnoses, for instance glucose tests for diabetes, thyroid function tests, or a head MRI if tumours are suspected.


  • In many cases, the problem is due to medication being used for another condition. Unless the drug is essential, it may be withdrawn or replaced with a different one, having fewer sedative effects.
  • Previously undiagnosed problems must be managed, like liver problems.
  • Advice about lifestyle changes and sleep hygiene may be useful.
  • Narcolepsy is managed by education about sleep management, and three useful medications, used under specialist supervision only:
    • Modafinil
    • Methylphenidate
    • Some amphetamines.


    Most patients with drowsiness can be successfully managed. Narcolepsy cannot be cured, but many patients can be helped to lessen their daytime drowsiness to manageable levels.

    Source: Dr A G Hall, (B.Soc.Sc.(SW), MB,Ch.B)

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