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Alternate Names

  • sleepiness


Drowsiness is a state of decreased awareness or alertness associated with a desire or tendency to fall asleep.

What is going on in the body?

Almost everyone has felt drowsy before, usually due to normal tiredness from a long day or lack of sleep. There are other causes of this condition as well. Most of the causes are not serious, but some are life threatening.


What are the causes and risks of the condition?

There are many possible causes of this condition, including:
  • lack of sleep or sleep disorders, such as insomnia and sleep apnea. Sleep apnea is a disorder of breathing during sleep that prevents a person from getting enough rest.
  • infections, such as chronic bronchitis or infectious mononucleosis
  • a low red blood cell count, called anemia
  • stress
  • working, studying, or exercising too much
  • lack of exercise or poor physical conditioning
  • hormone imbalances, such as hypothyroidism, a condition caused by a low level of thyroid hormone
  • depression or other psychological disorders
  • autoimmune disorders, that is conditions in which a person's immune system attacks his or her own body. Examples include systemic lupus erythematosus and rheumatoid arthritis.
  • low oxygen levels in the blood, which can occur with heart disease or chronic obstructive pulmonary disease
  • toxin or chemical exposure, such as carbon monoxide poisoning
  • medications, such as antihistamines, sedatives, and certain medications used to treat depression or high blood pressure
  • alcohol
  • systemic disorders, such as uncontrolled diabetes
  • a stroke, ("brain attack")
  • any severe, life-threatening illness, such as meningitis, severe pneumonia, or end-stage cancer
Other causes are also possible. Sometimes no cause can be found.


What can be done to prevent the condition?

Avoiding stress and overexertion, getting enough sleep, and eating a healthy diet can prevent many cases of drowsiness. Avoidance of alcohol and medications that cause drowsiness can avoid cases due to these causes. Maintaining a normal weight and avoiding obesity can sometimes prevent sleep apnea. Many causes cannot be prevented.


How is the condition diagnosed?

After a physical examination, the healthcare professional may order further tests. A chest x-ray may be done if lung disease is thought to be the cause. A sleep study, called polysomnography, may be done if sleep apnea is suspected. A complete blood count (CBC) may be ordered if anemia or an infection is suspected. Other tests may also be needed in some cases.

Long Term Effects

What are the long-term effects of the condition?

Drowsiness, when persistent, can limit a person's ability to work, go to school, and drive. Severely affected people may need to rest for most of the day. Other long-term effects depend on the cause. For instance, end-stage cancer often results in death. Cases due to a stroke may cause permanent drowsiness and other limitations from brain damage.

Other Risks

What are the risks to others?

Drowsiness is not contagious and poses no risk to others. However, if the cause is an infection, such as meningitis, the infection may be contagious.


What are the treatments for the condition?

Specific treatment is directed at the cause. For instance, a person may need to get antibiotics for an infection or thyroid hormone medication for a low thyroid level. In others, control of diabetes or other systemic disorders may be needed. A person with depression often needs medications to treat the condition. Those with cancer may need surgery, chemotherapy, or radiation therapy.

Side Effects

What are the side effects of the treatments?

All medications and surgeries have possible side effects. For instance, antibiotics may cause allergic reactions and stomach upset. Surgery can be complicated by bleeding, infection, or reactions to anesthesia.

After Treatment

What happens after treatment for the condition?

If the drowsiness goes away, a person may or may not need further treatment. For instance, those with kidney failure need further treatment even if their drowsiness goes away. Those who were "overdoing it" or not getting enough sleep may need no further treatment once they get some rest. Those with serious diseases, such as end-stage cancer, may die if treatment is unsuccessful.


How is the condition monitored?

Any new or worsening symptoms should be reported to the healthcare professional. The cause of drowsiness may or may not need monitoring. For instance, those with anemia need a repeat CBC to make sure the blood count has returned to normal.


Harrison's Principles of Internal Medicine, 1998, Fauci et al.

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