Understanding Why: What Causes Fainting and Trouble Breathing?

September 29, 2025 •

4 min read

According to the National Institutes of Health, syncope (fainting) accounts for 1-3% of all emergency department visits in the U.S.. When this temporary loss of consciousness is combined with respiratory distress, it begs the question: What causes fainting and trouble breathing?

Quick Summary

A combination of fainting and difficulty breathing can stem from various underlying issues affecting the cardiovascular or respiratory systems, including heart problems, anxiety or panic attacks, dehydration, and low blood sugar. It can be a medical emergency, so prompt evaluation is critical to determine the cause and get proper treatment.

Key Points

Cardiovascular Causes: Heart conditions like arrhythmias, heart failure, and pulmonary embolism can cause fainting and trouble breathing by disrupting blood flow and oxygen supply.
Anxiety and Panic: Intense anxiety can trigger hyperventilation and a stress response, leading to a feeling of breathlessness and lightheadedness that may cause fainting.
Low Blood Sugar: Hypoglycemia can trigger the release of stress hormones and affect muscle function, causing a rapid heartbeat, perceived shortness of breath, and, in severe cases, loss of consciousness.
Dehydration: Severe dehydration reduces blood volume, leading to low blood pressure, increased heart rate, and insufficient oxygen to the brain and lungs, which can cause fainting and breathing difficulties.
Medical Emergency: The combination of fainting and trouble breathing can indicate a serious condition and should always be evaluated by a healthcare professional immediately.
Distinguishing Symptoms: It is crucial to be able to distinguish between symptoms of a panic attack and a heart attack, although immediate medical help is necessary for either if symptoms are severe.

Causes of Fainting and Trouble Breathing

Experiencing a loss of consciousness (syncope) alongside difficulty breathing (dyspnea) is a serious combination of symptoms that requires careful attention. The underlying causes can range from relatively benign conditions like a vasovagal response to life-threatening medical emergencies such as a heart attack or pulmonary embolism. Understanding the potential reasons is crucial for knowing when to seek immediate medical help.

Cardiovascular Conditions

Many heart-related issues can lead to both fainting and trouble breathing because they disrupt the body's ability to pump oxygenated blood effectively to the brain and lungs. Without sufficient blood flow, the brain is deprived of oxygen, leading to fainting.

Heart Attacks and Heart Failure

A heart attack occurs when blood flow to a part of the heart muscle is blocked, while heart failure is a chronic condition where the heart is too weak to pump blood efficiently.

Heart Attack: Symptoms can include chest pain, shortness of breath, and feeling dizzy or weak, which can lead to fainting.
Heart Failure: As the heart's pumping ability weakens, fluid can build up in the lungs, causing shortness of breath. The reduced circulation can also decrease blood flow to the brain, resulting in dizziness and fainting.

Arrhythmias

Arrhythmias are irregular heart rhythms, where the heart may beat too fast (tachycardia) or too slow (bradycardia).

When the heart beats too fast or too slowly, it can impair blood circulation throughout the body.
This can lead to a drop in blood pressure, causing dizziness, lightheadedness, and fainting.
Shortness of breath may also occur as the heart struggles to meet the body's demands.

Pulmonary Embolism

A pulmonary embolism is a blockage in a lung artery, most often caused by a blood clot from a vein in the legs. This is a medical emergency.

A large clot can severely impede blood flow to the lungs, causing sudden shortness of breath and chest pain.
The resulting drop in blood pressure can cause the person to feel dizzy and faint.

Psychological and Neurological Factors

Not all causes are purely physical. Certain psychological and neurological conditions can also trigger a combined episode of fainting and respiratory distress.

Anxiety and Panic Attacks

During an intense anxiety or panic attack, a person may hyperventilate, leading to an imbalance of oxygen and carbon dioxide.

Hyperventilation: Breathing too quickly can lead to a drop in carbon dioxide, causing lightheadedness and feeling faint.
Stress Hormones: The body releases stress hormones that can cause a rapid heart rate and a sensation of being unable to breathe.

Vasovagal Syncope

This is the most common type of fainting and is typically not serious. It is an overreaction by the body to a specific trigger.

Triggers: These can include emotional stress, severe pain, the sight of blood, or prolonged standing in a hot environment.
Response: The vagus nerve overreacts, causing a sudden drop in heart rate and blood pressure, leading to fainting. While trouble breathing is not a primary symptom, the intense stress or fear associated with the trigger can cause a person to feel breathless.

Other Systemic Issues

Several other health problems can contribute to the co-occurrence of these two symptoms.

Hypoglycemia (Low Blood Sugar)

In diabetic individuals, low blood sugar can trigger the release of stress hormones, causing a rapid heartbeat and shallow breathing.

Severe hypoglycemia can lead to confusion, weakness, dizziness, and loss of consciousness.
The combination of a fast heart rate and shallow breathing can be perceived as trouble breathing.

Dehydration

When severely dehydrated, the body loses significant fluid volume, which can lead to a drop in blood pressure.

Hypotension: This lower blood pressure can cause insufficient blood flow to the brain, leading to dizziness, lightheadedness, and fainting.
Tachycardia: The heart rate may increase to compensate for the lower blood volume, which can be accompanied by shortness of breath.

Comparison: Heart Attack vs. Panic Attack

Many people confuse panic attack symptoms with a heart attack. Here is a comparison to help differentiate the two.


Symptom	Heart Attack	Panic Attack
Onset	Can be gradual or sudden; often during exertion.	Often sudden, seemingly out of nowhere; can be triggered.
Chest Pain	Pressure, squeezing, or a crushing sensation; may radiate to the arm, neck, or jaw.	Sharp or stabbing pain, localized to the center of the chest.
Shortness of Breath	Typically happens with exertion or due to heart failure.	Common, often accompanied by hyperventilation.
Associated Symptoms	Fatigue, nausea, and sweating.	Intense fear, feeling of impending doom, trembling, tingling.
Duration	Can last for several minutes or come and go.	Typically peaks within 10 minutes and subsides.
Key Differentiator	Risk factors like age, family history, and underlying heart conditions.	Often associated with anxiety disorders and specific triggers.

When to Seek Immediate Medical Attention

Because of the overlap in symptoms, it can be difficult to distinguish between a benign event and a medical emergency. If you or someone you know experiences a combination of fainting and trouble breathing, seek emergency medical care immediately. Never assume the cause is benign without professional medical evaluation. The following signs warrant an emergency room visit:

Fainting that occurs during exercise or physical exertion.
Fainting accompanied by severe chest pain, jaw pain, or arm pain.
Feeling short of breath that doesn't resolve quickly.
A rapid, irregular, or pounding heartbeat.
Sudden dizziness or loss of consciousness.
A pre-existing heart condition.

Conclusion

The simultaneous occurrence of fainting and trouble breathing is a symptom complex that should never be ignored. While it can sometimes be attributed to less severe causes like anxiety or vasovagal responses, the potential for serious underlying conditions, particularly involving the cardiovascular system, is too high to risk. An accurate diagnosis from a healthcare professional is the only way to determine the root cause and ensure appropriate action is taken. Timely medical attention can be life-saving. For further information on syncope, you can visit the National Institutes of Health website.

Frequently Asked Questions

Yes, very low blood pressure (hypotension) can cause fainting by reducing blood flow to the brain. In severe cases, particularly if the low pressure is related to dehydration or a heart issue, it can also cause a compensatory increase in heart rate and breathing, leading to a sensation of trouble breathing.

While it can be difficult to distinguish, a panic attack is often accompanied by an overwhelming sense of dread, tingling, and a sharp, localized chest pain. A heart attack may involve crushing chest pressure that radiates to the arm or jaw, accompanied by nausea or cold sweats. If in doubt, always seek immediate medical evaluation.

Vasovagal syncope is generally benign, but the accompanying symptoms should not be ignored. While not the primary mechanism, the intense emotional or physical stress triggering the event can cause a sense of breathlessness. However, if the fainting is recurrent or occurs during exercise, it warrants a doctor's visit to rule out a cardiac cause.

Yes, severe dehydration can lead to a dangerously low blood volume and pressure (hypotension). This can cause dizziness, lightheadedness, and fainting due to reduced blood flow to the brain. The body's compensating mechanisms may also cause a rapid heart rate and shortness of breath.

A pulmonary embolism is a life-threatening blood clot that travels to the lungs, blocking a pulmonary artery. This obstruction prevents oxygen from being absorbed into the blood. This lack of oxygen and the resulting strain on the heart cause sudden chest pain, shortness of breath, and can lead to a drop in blood pressure and fainting.

Yes, although it is less common. Hypoglycemia can occur in non-diabetics due to certain medications, excessive alcohol consumption, or other medical conditions. The body's stress response to low glucose can cause a rapid heartbeat and symptoms mimicking anxiety, which can lead to feeling faint and breathless.

You should go to the emergency room immediately if fainting is accompanied by chest pain, a feeling of an irregular or very fast heartbeat, shortness of breath that doesn't improve, or if the fainting happens without any clear trigger. Any episode of fainting, especially if it's the first time or if you have a pre-existing heart condition, should be medically evaluated.