Peter Goldstein has always been freaked out by needles and blood.

When he was about 5, his mother, physician Susan Wiegers, had a small biopsy done. Goldstein and his brother asked to see the wound. "It was a tiny line with two stitches," she recalled. Goldstein's brother was fascinated. But Goldstein turned away. Then he keeled over.

Since then, he's passed out every time he's had a close encounter with a syringe. At the sight of blood, he has to quickly drop his head below his knees. He recently felt woozy just listening to his mother describe someone in a cast. "It's not rational," said Goldstein, 28, who's a quantitative finance researcher in New York. "I can watch gory movies without a problem."

It's fairly common for people to faint from needle phobia — although the problem is neither the needles nor the fear.

"Most people are anxious when they are faced with being stuck with needles," said Dr. Joshua Cooper, director of cardiac electrophysiology for Temple's Heart and Vascular Center. "It's not that some people are more afraid than others and that's why they faint. It's that they are wired such that they have a powerful vasovagal reflex."

The reflex, which can cause fainting, may be triggered by fear, pain or a number of other causes, including standing in church for a few hours, said Cooper.

"Up to 20 percent of people have an inappropriate nerve reflex, where the brain inappropriately sends a very strong signal down the vagus nerve," he said.

The vagus is the longest of the 12 cranial nerves. A main branch of the parasympathetic nervous system, the vagus starts in the brain, runs down the neck and branches through the body to the heart and blood vessels. When the brain sends a signal down the vagus, it slows the heart rate and lowers blood pressure by dilating or expanding blood vessels.

"Moment to moment, the brain is always using the vagus and sympathetic nerves to adjust heart rate and blood pressure to be appropriate to what you're doing," said Cooper.

When panic or fear triggers a surge of adrenaline, that causes the heart to race and the blood pressure to rise, Cooper said. In those prone to vasovagal syncope, "the brain gets the message that the heart is working too hard. The brain tries to counteract that, but overdoes it, dropping the heart rate and blood pressure."

In most cases, these occasional fainting episodes are harmless, but if they happen regularly, it might indicate a problem with heart arrhythmia or other cardiac conditions.

Limiting options

"Regular fainting can be debilitating for some patients," said Dr. Mark Linzer, director of the division of general internal medicine at Hennepin County Medical Center. For decades he's worked with patients who struggle with fainting.

Patients may have trouble doing daily activities like driving, or may not drive altogether, out of fear of fainting, he said.

While Linzer said a powerful vasovagal reflex may be one answer, the question of why people faint at the sight of needles continues to puzzle researchers.

The confusion limits how doctors can help patients in controlling their episodes.

The predicament is particularly inconvenient for health care workers who cannot look at a needle coming their way without sending themselves into a head-spinning vortex.

"It is an interesting problem," Wiegers said. "When you look at a group of doctors and find out why they didn't get the flu shot in hospitals where there is strong pressure to get it, you find out that it is because most of them are afraid of shots or pass out."

Flu shot fears

While Christopher Gonzalez has no problem watching other people get shots, he cannot even think about getting one himself without panicking. His heart races. He gets cold and clammy.

"It's the worst," said Gonzalez, a surgical coordinator for Pennsylvania Orthopaedic Foot and Ankle Surgeons in Philadelphia. As part of hospital staff, Gonzalez, 24, has tried everything to buck himself up for the annual flu shot.

He has rolled up his own sleeve to trick himself into thinking he's in control, aimed his focus fiercely on ceiling tiles to distract himself, and given himself upbeat pre-puncture talks.

Nothing works.

So he asked, with all his persuasive power, for special dispensation.

Not happening, he was told. "I work here, so I have to get it. I try to be the last one to go," he said. "The shot is never as bad as the anxiety that precedes it."

"Then they give me a Band-Aid and call it a day."

Eric Best contributed to this report.