Vasovagal syncope, illustration. Vasovagal syncope, or vasovagal fainting, is caused by an over-reaction of the vagus nerve (yellow) that results in a sudden drop in blood pressure and heart rate. Common triggers include extreme heat, fear, pain, the site of blood and also standing still for an extended period of time. Symptoms before fainting may include nausea, dizziness and blurred vision. Consciousness is usually regained quickly. Vasovagal syncope is most common form of fainting and is usually harmless.