Vasovagal Hypotension

The vagus nerve is a nerve that helps regulate the heart rate and the blood vessels. In vasovagal hypotension, certain triggers make this nerve reflex overreact: the blood vessels in the legs and abdomen suddenly widen, and the heart rate slows. Blood pressure drops suddenly, blood flow to the brain decreases, and you may faint for a few seconds to less than a minute. When it leads to fainting, the condition is called vasovagal syncope, a type of fainting that many people experience, especially teenagers and young adults.

Triggers and Warning Signs

Common triggers include standing for a long time, for example at a ceremony or in a queue, hot and crowded rooms, not drinking enough, hunger, lack of sleep, pain, fear, the sight of blood or needles, and the moments after straining, hard coughing, or urinating. Before fainting, there are usually warning signs lasting a few seconds to minutes: lightheadedness, nausea, sweating, feeling hot, narrowing or darkening vision, and ringing in the ears. People nearby often notice that the face turns pale.

Why It Is Usually Not Dangerous

Once the body falls or is laid down, blood returns to the brain more easily, so consciousness comes back quickly. After waking up, you usually recognize the place and the people around you right away, although you may still feel tired, nauseated, or pale for a while. Some people have a few brief muscle jerks while fainting, which does not mean an epileptic seizure. Vasovagal hypotension does not indicate heart disease and does not damage the heart. The main risk is injury from falling. In a small number of people, frequent repeated fainting can interfere with school, work, or driving.

Even so, a first faint still needs to be checked by a doctor, because fainting can also be caused by rhythm disorders or structural heart disease, which are treated differently. Fainting in general is covered on the Syncope page. Vasovagal hypotension is one type of hypotension, which is covered on the Hypotension page.

The main treatment is understanding this condition, recognizing triggers and warning signs, and then doing counterpressure maneuvers or lying down right away when those signs appear. Medicines or a pacemaker are considered only for a small number of people with severe recurrent fainting.

The key to diagnosis is a complete account, from you and from anyone who saw what happened: your position when you fainted, the trigger, the warning signs, how long you were unconscious, and how you felt after waking up. The doctor also asks about any history of heart disease, your medicines, and any family history of sudden death. The physical examination includes blood pressure lying down and standing up, as well as a heart examination. An ECG is done for everyone who faints to look for rhythm disorders or signs of heart disease.

If the account is typical and the ECG is normal, the diagnosis can often be made without other tests. If it is still unclear, the doctor may do a tilt table test, echocardiography, a heart rhythm recording over several days, or a rhythm recorder placed under the skin for fainting that is infrequent but recurrent.

Any first-time faint needs to be checked by a doctor to confirm that the cause is the vasovagal reflex and not a heart problem. Also see a doctor if any of the following apply to you.

• Fainting that recurs or becomes more frequent
• Fainting that causes an injury
• Fainting without warning signs or while lying down
• Fainting during exercise, or preceded by palpitations or chest pain
• A family member who died suddenly at a young age
• Work as a driver or in a place where fainting would be risky