Most types of specific phobia cause the heart rate and blood pressure to rise.
Hemophobia and other blood-injection-injury phobias frequently cause a drop in blood pressure and heart rate. The sudden drop can lead to fainting, a relatively common response to the sight of blood. Anticipatory anxiety, in which you may experience a racing heart, shaking, and gastrointestinal distress, is common in the hours and days before an upcoming encounter with blood.