There are thousands of real-life vampires walking in the USA.

At least 5,000 self-identified, blood-drinking vampires — people who consume human and animal blood because they feel that they need it to survive — live in the U.S., according to the Atlanta Vampire Alliance.

Most of those people are otherwise “normal” — loving husbands and wives, dedicated mothers and fathers, loyal employees — vampire expert John Edgar Browning, who has spent five years studying the population, told the Washington Post.

“After a short period of time, I realized that they weren’t crazy,” he said. “At least, they weren’t any crazier than your Average Joe.”

Each vampire has his or her way of “feeding” on blood, Browning said. Their donors — people who allow a vampire to collect their blood and drink it — are often close friends who give up their plasma pro-bono. Other times, vampires pay their givers or reward them with sexual favors.

Browning, a postdoctoral fellow at the Georgia Institute of Technology, once served as a donor during his five-year study on the New Orleans vampire population, which includes about 50 self-identified bloodsuckers.

The vampire swabbed his back with an alcohol pad, made a tiny prick in his back with a scalpel and lapped up the fluid, Browning said. The pair went to a New Orleans Vampire Association charity dinner after the feeding.

The vampires Browning interviewed during the study said they get a certain kind of energy from drinking blood: They can go from feeling drained to rejuvenated with just a small sample of hemoglobin. On average, they feed two or three times a week, he said.

None of the vampires know why they need blood. Many keep the secret from their doctors, fearing ridicule.

But they claim they have very real consequences when they go without the red stuff.

“One scary moment was when I was admitted to ER for having a low heart rate that would jump up to 160 when I stood up, or walked around, followed by a massive migraine, and often losing consciousness,” a vampire named Kinesia told the BBC.

She continued: “Basically, my heart was working extra hard to keep everything functioning — a reaction, I believe, to about four months without feeding.”

Some vampires don’t drink blood, instead harvesting energy from others through physical touch. There are as many as 10,000 non-blood drinkers in the U.S. on top of the 5,000 who consume plasma, the Atlanta vampire group found.