Causes a Loss of Consciousness

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

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.

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

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

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.

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

A migraine attack.

The lowering of sugar in the blood, or hypoglycaemia.

Alcohol consumption and abuse of other drugs.

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

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

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

Disease of the heart muscle (cardiomyopathy).