Can pulmonary embolism cause dizziness or fainting? 

A pulmonary embolism occurs when a blood vessel in your lung becomes blocked, usually by a blood clot that has travelled from elsewhere in the body. While many people associate this condition with chest pain or breathing difficulties, dizziness and fainting are also recognised symptoms. These sensations can indicate that the heart and lungs are under significant strain, making it important to understand why they happen and how to respond safely according to UK medical standards. 

What We’ll Discuss in This Article 

• Whether dizziness and fainting are common symptoms of pulmonary embolism. 

• The physiological reasons why a lung clot affects blood pressure and consciousness. 

• How to recognise fainting (syncope) as a potential medical emergency. 

• Other primary symptoms that often appear alongside lightheadedness. 

• The connection between leg clots and sudden changes in consciousness. 

• When and how to seek immediate emergency medical help in the UK. 

Dizziness and fainting are serious symptoms that can indicate a pulmonary embolism 

Dizziness, lightheadedness, and fainting, medically known as syncope, are established symptoms of a pulmonary embolism. These symptoms occur when a blood clot is large enough to obstruct significant blood flow through the lungs, which in turn reduces the amount of oxygenated blood the heart can pump to the rest of the body, including the brain. Fainting is often seen as a sign of a more extensive blockage that requires immediate clinical assessment. 

The NHS states that feeling faint, dizzy, or passing out can be symptoms of a pulmonary embolism. When these sensations happen suddenly, especially if they are accompanied by breathlessness or chest pain, they are considered high priority indicators of a circulatory issue. In some cases, a brief period of unconsciousness may be the first or only obvious sign that a person is experiencing a pulmonary embolism. 

Why a pulmonary embolism leads to changes in consciousness 

The primary reason a pulmonary embolism causes dizziness or fainting is a sudden drop in blood pressure and a decrease in oxygen delivery to the brain. When a clot blocks a pulmonary artery, the right side of the heart must work much harder to push blood through the lungs. If the blockage is substantial, the heart may struggle to maintain enough output to keep blood pressure stable. 

This lack of stable blood flow means the brain temporarily does not receive the oxygen it needs to maintain consciousness. This is different from a typical “faint” caused by heat or standing up too quickly, as the underlying cause is a physical obstruction in the cardiovascular system. NICE clinical guidelines highlight that syncope is a specific clinical feature used to assess the severity of a suspected pulmonary embolism. 

Recognising fainting as a potential emergency signal 

Fainting associated with a pulmonary embolism often occurs abruptly and may be preceded by a feeling of a racing heart or sudden shortness of breath. Because the body is struggling to compensate for a blockage, the recovery from this type of fainting may feel different than a standard vasovagal faint. A person may remain breathless, pale, or have a persistently high heart rate even after they have regained consciousness. 

In the context of a lung clot, fainting is often a marker of hemodynamic instability. This means the circulatory system is having difficulty maintaining the necessary pressure to function. Healthcare professionals in the UK treat any unexplained loss of consciousness alongside respiratory distress as a critical event, as it suggests the heart is under significant pressure. 

Other symptoms that may occur with dizziness 

Dizziness and fainting are rarely the only symptoms present when a pulmonary embolism occurs. Most people will also experience a sudden onset of shortness of breath, which can feel like an inability to catch one’s breath even while sitting still. Sharp chest pain that feels worse when breathing in, coughing, or sneezing is another very common sign that usually accompanies the lightheadedness. 

Symptom	Description
Shortness of Breath	Sudden difficulty breathing or feeling “winded” without exertion.
Sharp Chest Pain	Stabbing pain that worsens with deep breaths or coughing.
Rapid Heartbeat	Feeling like the heart is racing, fluttering, or thumping.
Coughing	A persistent cough, sometimes producing blood-streaked mucus.

The link between leg symptoms and fainting episodes 

A pulmonary embolism usually originates as a blood clot in the deep veins of the leg, known as deep vein thrombosis (DVT). If a person has recently experienced swelling, redness, or pain in one leg and then suddenly feels dizzy or faints, the clinical suspicion of an embolism is greatly increased. The clot in the leg can break loose and travel to the heart and lungs, causing the sudden drop in blood pressure that leads to fainting. 

According to the NHS, pain and swelling in one leg are key warning signs that a clot may have formed and could travel to the lungs. Identifying this connection is a vital part of the diagnostic process in UK hospitals. Risk factors such as recent surgery, long periods of immobility, or long-distance travel should be mentioned to medical staff if dizziness or fainting occurs. 

Conclusion 

Pulmonary embolism can cause dizziness or fainting because the blockage in the lung arteries prevents enough oxygenated blood from reaching the brain. These symptoms often signal a significant blockage and usually occur alongside sudden breathlessness and sharp chest pain. Recognising fainting as a serious warning sign, especially when combined with respiratory distress or leg swelling, is essential for ensuring a safe and rapid medical response. 

If you experience severe, sudden, or worsening symptoms, call 999 immediately. 

Authority Snapshot (E-E-A-T Block) 

This guide was created to provide the public with clear, factual information on how pulmonary embolism can affect consciousness and blood pressure. It has been authored and reviewed by Dr. Stefan Petrov, a UK-trained physician with extensive experience in emergency care and general medicine. The content is strictly aligned with clinical guidelines from the NHS and NICE to ensure accuracy and patient safety.