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You are here : 3-RX.com > Medical Encyclopedia > Diseases and Conditions > Loss of Consciousness
      Category : Health Centers > Brain and Nervous System

Loss of Consciousness

Alternate Names : Unconsciousness

Overview, Causes, & Risk Factors | Symptoms & Signs | Diagnosis & Tests | Prevention & Expectations | Treatment & Monitoring

Consciousness is the state of being aware of or responsive to the environment. A person who is conscious can perceive, both physically and mentally, what is happening. For many reasons, a person can sometimes lose consciousness, or become unconscious.

What is going on in the body?

An unconscious person generally seems to be sleeping. However, being unconscious is different from being asleep. A person can usually, but not always, be roused from the unconscious state.

What are the causes and risks of the condition?

There are many causes of unconsciousness, including:

  • fainting, which may occur in healthy, normal people. It often results from fatigue, pain, injury, or strong emotions such as fear. It is also common during pregnancy. Someone who faints usually wakes up within 2 minutes. Most of the time, there are no lasting problems associated with a fainting episode.
  • low blood pressure, also called hypotension. This can occur for many reasons. High blood pressure medications, serious blood loss, and dehydration are all possible causes. Orthostatic hypotension, a condition in which the blood pressure drops quickly when the person stands up, can also cause fainting.
  • medication, drug, or toxin exposure. This can include overdose with alcohol, barbiturates, or narcotics.
  • head injury. This may be mild in the case of a concussion, or more serious, as in the case of a skull fracture.
  • stroke, also called brain attack. This is brain damage that usually occurs due to a lack of oxygen. A transient ischemic attack or TIA is another cause of unconsciousness.
  • bleeding into or around the brain, which occurs with a subdural hematoma, epidural hematoma, or subarachnoid hemorrhage
  • infections, such as the brain infections called meningitis and encephalitis
  • low blood sugar levels, called hypoglycemia
  • diabetes that is out of control
  • severe liver disease or kidney disease
  • seizures, or jerking movements caused by abnormal electrical activity in the brain
  • low oxygen level in the blood, which can occur with severe lung or heart disease. For example, severe asthma, emphysema, irregular heartbeats called arrhythmias, severe congestive heart failure, or a blood clot in the lung, called a pulmonary embolus, can all cause low oxygen levels in the blood.
  • abnormally low body temperature, also called hypothermia
  • severe salt imbalances, such as abnormally low or high sodium levels in the blood
  • brain tumors


    Next section


    Loss of Consciousness: Symptoms & Signs

    Author: Adam Brochert, MD
    Reviewer: Eileen McLaughlin, RN, BSN
    Date Reviewed: 07/12/01

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