Lee says the paranormal shows have created "mass hysteria" -- people think something paranormal is going on in their home when the explanation is often mundane.
"We will often get a call with clients that are convinced that the dust particles in their photographs are actual demons," Lee says.
Some investigators say that there are times, though, when they encounter something that is terrifying.
Lee says her team met a single mom who was being "oppressed by some type of demonic activity." A priest was called in to perform an exorcism.
"When he arrived, the client's eyes were all black," she says. "The eyes were crystal blue when the priest finished."
Lee says she didn't sleep for weeks after that case, which was eventually filmed by the Discovery Channel as "The Exorcism of Cindy Sauer" (It's on YouTube).
"You never know what you're going to walk into," Lee says. "I have never seen anything like that in my life. I thought maybe I shouldn't do this."
John Zaffis, a paranormal investigator for 38 years, has walked into his share of strange situations. He's been dubbed the "Godfather of the Paranormal" and hosts the television show "Haunted Collector." He's Lorraine Warren's nephew, and his investigations have been featured on the Discovery Channel and "Unsolved Mysteries."
Zaffis says he's been attacked.
"I've been scratched, I've been burned. I've seen people levitate. I've seen people's eyes change, and I've seen people thrown around," he says. "That changes how you look at things."
Noah Voss, a paranormal investigator for 25 years who sells ghost-hunting equipment at GetGhostGear.com, says the job requires not just courage, but sensitivity as well. People share experiences with him that they don't even reveal to their spouses.
"I've had guys bigger than me break down and cry, saying to me that they can't go back into their house because it's haunted," says Voss, who is 6-feet-4 and more than 200 pounds.
But Voss and others say those moments of terror are not routine. Some compare it to fishing: There's a lot of preparation, but nothing usually happens. It's not like TV, where a ghost appears in every episode.
Some of the newer ghost-hunting groups aren't prepared for the mundane nature of actual paranormal investigations and worry that they might miss out on their big chance, Voss says. "People will say, 'My group has been investigating for six months and we still haven't had our own TV show.'"
Some inexperienced teams give new meaning to taking their work home with them, says "Uninvited" author LaChance.
"Novice teams will try to provoke spirits, and the next thing you know these things follow them home," he says. "About two years ago, we had more investigative teams calling us to help them than individual families. It was crazy."
LaChance wishes he did not believe in the paranormal.
He investigated one case involving a couple's 50-pound pit bull. The couple had treated their dog like it was their child. But when he showed up, the dog was inside its cage, dead. Blood was everywhere. He says an entity had thrown the dog, cage and all, down the hall and killed it.
Like some other paranormal investigators, LaChance talks about his work like it's a ministry. Many ghost-hunting teams don't charge for investigations. They see their work as a way to help people in distress.
"It has to do with helping someone else who is in the same situation I found myself in at one time," he says, recalling the house where he says malevolent spirits attacked his children. "When I went looking for help back when I needed it, I could not find it."