Loss Of Consciousness: Why Does It Happen?

Loss of consciousness is a relatively common clinical problem. The reasons for this can be simple or life threatening. In this article we explain why it can happen in detail.
Loss of consciousness: why does it happen?

Loss of consciousness is also known as fainting. It is simply a disconnection from reality. The person who suffers from it loses the perception of what is going on around them as well as the perception of himself.

Lack of proper blood supply to the brain is the basic mechanism that is common to all causes. This means that your brain does not get enough blood for a moment, which causes a disconnection from reality. Usually the person spontaneously recovers. Spontaneous improvement occurs because the horizontal position when the person falls favors the arrival of blood to the brain.

Fainting is relatively common. It is estimated that three percent of all emergency consultations are due to this. The reasons behind this can be serious or harmless. Below we will explain more about this and divide the causes into two different categories: non-heart-related loss of consciousness and heart-related loss of consciousness.

Non-heart-related causes of loss of consciousness

Vasovagal syncope

This is the most common cause. Vasovagal syncope is an involuntary response from the nervous system to a given stimulus that causes immediate vasodilation, a drop in blood pressure and redistribution of blood to the legs. Sometimes it is also caused by a stressful situation as well as intense body aches, dehydration and extreme temperatures.

Changes in positions

When you quickly switch between a horizontal and a vertical position without giving the body enough time to activate the compensation mechanisms, you may suffer from hypotension. This means that the blood pressure drops, which leads to a lack of blood supply in the brain.

Migraines can cause loss of consciousness

Intense headaches and migraines may be accompanied by symptoms known as auras. One of the auras of migraines is loss of consciousness, but it is usually temporary.


A drop in blood sugar levels can also cause fainting. This situation is common among diabetics who may suffer from extreme drops in blood sugar levels due to dietary changes or medications.

Blood pressure medications

A person suffering from hypertension is usually medicated with several medications with different mechanisms of action. Some of the mechanisms of action of these substances are fluid loss through increased urination and vasodilation. Both of these processes can drastically lower blood pressure and cause loss of consciousness.

Stroke and loss of consciousness

This is the most serious and life-threatening non-heart-related cause. A stroke or cerebrovascular accident (CVA) can be ischemic, due to a blockage in the arteries, or hemorrhagic, due to a damaged cerebral vessel. If you think that you or someone you know is suffering from the symptoms of a stroke , you need to see a doctor immediately.

A man with a headache.
Heart disease can manifest itself with this symptom.

Heart-related causes of loss of consciousness


Arrhythmias are conditions in which the heart beats irregularly and abnormally. Given these irregular heartbeats , not enough blood will reach the brain for a short or long period of time. The patient may therefore faint.

Aortic problems

The aorta is the body’s most important artery and it is responsible for distributing the blood to the rest of the body. If this artery has a problem, blood flow to the rest of the body can be reduced. Since the brain is above heart level, it requires good blood pressure for proper blood flow. Loss of consciousness is often the first symptom of diseases such as aortic dissection or aortic aneurysms.


These conditions affect the heart muscle. A common situation is that the left ventricle, which is responsible for pumping blood into the aorta for distribution, enlarges. In these cases, the same problem that we described under aortic problems may occur.

Heart valve diseases

The inner cavities of the heart communicate with each other through valves that allow blood to flow in one direction, without backflow. Sometimes these flaps are defective or more closed than they should be. When they do not do their job, not enough blood will reach the brain.

A digital representation of the heart.
Heart disease can manifest itself with this symptom.

What do you do after losing consciousness?

As we have seen, you must always be vigilant in the presence of the various causes behind loss of consciousness. This is because there may be a less severe loss of consciousness or the announcement of a heart disease.

If in doubt, it is important to consult a medical professional to get the necessary tests. The consultation usually takes place a short time after the incident and the patient has recovered.

If the loss of consciousness is sudden and without any immediate explanation and the person does not wake up again, you should call the emergency services. This may be a sign of a stroke or heart failure.

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