Loss of consciousness, why can it happen?

Loss of consciousness is also known as loss of consciousness. They are equivalent expressions in medicine and define the same clinical picture in one way or another.

Both definitions are valid because a loss of consciousness is a disconnection of consciousness with reality. The person who suffers it loses the perception of what is around him and the perception of himself.

The basic mechanism that is common to all causes of loss of consciousness is the lack of adequate cerebral irrigation. This means that not enough blood reaches the brain for a moment. and then the disconnection with reality occurs.

A special situation in the loss of consciousness is syncope, commonly known as fainting, since the person recovers spontaneously. Spontaneous recovery happens because when you faint, the horizontal body favors the arrival of blood to the brain. In strict terms, a syncope is a loss of knowledge of cardiac origin.

The picture is relatively frequent. It is estimated that in guard consultations, three percent corresponds to syncopes. Since its causes can be low risk or dangerous, we divide them here into non-cardiac and cardiac to explain them to you.

Non-cardiac causes of loss of consciousness

Vasovagal syncope

We start with the most frequent of all causes. The vasovagal reflex is an involuntary response of the nervous system to a certain stimulus, which pit causes immediate vasodilation, drop in blood pressure and redistribution of blood to the lower limbs.

Sometimes it is caused by a stress situation, also intense body aches, dehydration and extreme temperatures.

Posture Changes

When we quickly change from horizontal to vertical position, without giving the body time to activate compensation mechanisms, hypotension occurs.

That is blood pressure drops and blood, as in vasovagal syncope, is distributed to the lower limbs, stop properly irrigating the brain.


Intense headaches, of the migrainous type, may be accompanied by symptoms known as auras. Among the auras of migraine is the loss of consciousness, which is usually momentary.


The decrease in blood glucose values ​​can cause loss of consciousness. This situation is common among diabetics in treatment which, due to alterations in the diet or in the application of medication, cause their blood glucose levels to drop.


The person suffering from high blood pressure is usually medicated with different drugs of different action. Among the mechanisms of action of these drugs is the loss of fluid through increased urine and vasodilation.. Both processes can lower blood pressure too much and cause loss of consciousness.


Among the non-cardiac causes, it is the most serious, putting life at risk. Stroke or stroke can be ischemic –By an obstruction in the cerebral arteries- or hemorrhagic –by the rupture of a cerebral vessel.

Headache may be the initial symptom prior to loss of consciousness.

Continue reading: First symptoms of a stroke

Cardiac causes of loss of consciousness


Arrhythmias are diseases where the heart beats irregularly and abnormally. Faced with those irregular beats, the situation may occur that not enough blood reaches the brain for a moment, short or prolonged. There the loss of consciousness occurs.

Aortic problems

The aortic artery is the main artery of the organism, responsible for distributing the blood of the heart to the rest of the human body. If this artery has a problem, blood flow to the body may decrease.

Since the brain is above the level of the heart, it requires good blood pressure to be irrigated. Diseases such as aortic dissection or aortic aneurysms usually have the first symptom of loss of consciousness.

Cardiac myopathies

If the heart has altered the muscle that forms it, talk about cardiomyopathy. A common situation is that the area of ​​the left ventricle is enlarged, in charge of pumping the blood to the aorta to distribute it. In those cases the same mechanism that we describe when talking about aortic problems can happen.


The internal cavities of the heart communicate with each other through valves that allow blood to circulate in only one direction, without reflux. Sometimes these valves are insufficient or more closed than they should. By not doing his job, the amount of blood that will finally reach the brain suffers.

Heart disease can manifest itself with loss of consciousness.

Keep discovering: Heart disease not only affects the heart

What to do before a loss of consciousness?

As we have seen, given the varied causes of loss of consciousness that we can witness, it is always necessary to be attentive. It may be a banal fainting, without major repercussions, or be the warning of heart disease.

When in doubt, The important thing is to consult with a medical professional to perform the necessary complementary tests. Generally, the consultation takes place some time after having suffered the clinical picture, when the patient is recovered.

However, If the loss of consciousness is sudden, without immediate explanation and without recovery of the person when they pass out, then an emergency service should be called. It may be a stroke or heart failure.