Causes a Loss of Consciousness

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Syncope is caused by a temporary reduction in blood flow to the brain. This temporary reduction in the blood supply in the brain can be caused by heart diseases and, more commonly, due to other conditions that do not directly involve the heart.

Non-cardiac causes

Persistent cough

Vasovagal syncope. It is the most common cause. It is produced by an involuntary reflex of the nervous system. The causes of blackout are: after taking a blood sample; an intense pain, or after certain situations, such as to urinate, defecate, or cough intensely (situational syncope). This situation can also occur with extreme emotional stress, hunger and thirst

stretched man resting

Postural hypotension. It is the lowering of blood pressure due to a change from one body position to a more vertical position, after waking up or sitting down.

Bottle with cross line

Dehydration. Causes a decrease in blood volume, and thus, blood flow in the brain.

Green and white pills

Blood pressure drugs. They can lead to an excessive lowering of blood pressure at any time.

Nervous system extermidades, old people, problems in the legs

Diseases of the nerves of the legs in older people (especially with diabetes or Parkinson’s disease). When there is a lack of tonicity in the nerves of the legs, the blood does not return to the brain adequately.

brain with malformations

Stroke. Ischaemic stroke, cerebral stroke, transitory ischaemic attack. 

Central pain, anxiety

A migraine attack.

Low levels of sugar

The lowering of sugar in the blood, or hypoglycaemia.


Alcohol consumption and abuse of other drugs.

Cardiac causes


Abnormal heart rhythms (heart beats too fast or too slow).

Internal vision of the heart

Abnormalities of the heart valves (aortic stenosis or pulmonary valve stenosis).

obstructed artery

Disease of the aorta (aortic dissection due to aneurysms).


Damaged cardiac muscle

Disease of the heart muscle (cardiomyopathy).

Substantiated information by:

Elisenda Gómez-Angelats

Published: 20 February 2018
Updated: 20 February 2018


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