Have you ever fainted at the sight of a needle? You're not alone. Experts say that a fear of needles is actually a medical phobia, which can develop if you had a bad experience in a doctor or dentist's office before the age of 10. People who are terrified of needles get the same heart racing and shallow breathing seen in other intense fears, but the fainting sets medical phobias apart from, say, a fear of heights or spiders - where fainting is rare.So what makes you actually faint? Dr. Martin Antony is a psychology professor at Ryerson University. He says it's the vasovagal reflex that makes you pass out. Here's how it works: When you see a needle, it triggers a reaction in your vagus nerve, which widens your blood vessels, slows your heart rate, and drops your blood pressure. It happens so rapidly, you can lose consciousness for a few seconds. It tends to run in families, meaning, if your parent or sibling has the issue, you may, too.The bad part of having an extreme fear of needles is that it can affect your health, because people with full-blown phobias often refuse to see a doctor for medical tests. Or avoid insulin injections, immunizations, or having life-saving surgery. So if you have a needle phobia, how can you cope? Our expert says you'll need to see a therapist. The treatment progresses rather quickly, but you'll need to be exposed to your fears. You might start by talking about needles, then looking at pictures of them, and watching videos of people getting shots or being hooked up to IVs. Eventually, you'll work your way up to a real injection. If you're a fainter, your therapist will teach you a technique called "applied tension," where you tense your muscles before a shot to boost your blood pressure, which keeps you from fainting.