If youve ever fainted at the sight of your own blood, it could be due to a hard-wired response in your brain, according to researchers at the Center for Syncope and Autonomic Disorders. A condition called vasovagal syncope occurs when your blood pressure drops and reduces the flow of blood to the brain, therefore causing one to lose consciousness. This reflex can happen when faced with dehydration, emotional stress, anxiety, pain or fear and in some cases the sight of blood.