Vasovagal syncope (also called cardio-neurogenic syncope) Vasovagal syncope is the most common type of syncope. It is caused by a sudden drop in blood pressure, which causes a drop in blood flow to the brain. When you stand up, gravity causes blood to settle in the lower part of your body, below your diaphragm.
https://my.clevelandclinic.org/health/diseases/17536-syncope