(CNN) -- Nina De Santo was about to close her New Jersey hair salon one winter's night when she saw him standing outside the shop's glass front door.

It was Michael. He was a soft-spoken customer who'd been going through a brutal patch in his life. His wife had divorced him after having an affair with his stepbrother, and he had lost custody of his boy and girl in the ensuing battle.

He was emotionally shattered, but De Santo had tried to help. She'd listened to his problems, given him pep talks, taken him out for drinks.

When De Santo opened the door that Saturday night, Michael was smiling.

"Nina, I can't stay long," he said, pausing in the doorway. "I just wanted to stop by and say thank you for everything."

They chatted a bit more before Michael left and De Santo went home. On Sunday she received a strange call from a salon employee. Michael's body had been found the previous morning -- at least nine hours before she talked to him at her shop. He had committed suicide.

If Michael was dead, who, or what, did she talk to that night?

"It was very bizarre," she said of the 2001 encounter. "I went through a period of disbelief. How can you tell someone that you saw this man, solid as ever, walk in and talk to you, but he's dead?"

Today, De Santo has a name for what happened that night: "crisis apparition." She stumbled onto the term while reading about paranormal activities after the incident. According to paranormal investigators, a crisis apparition is the spirit of a recently deceased person who visits someone they had a close emotional connection with, usually to say goodbye.

Reports of these eerie encounters are materializing in online discussion groups, books such as "Messages" -- which features stories of people making contact with loved ones lost on September 11 -- and local ghost hunting groups that have sprung up across the country amid a surge of interest in the paranormal.

Although such encounters are chilling, they can also be comforting, witnesses and paranormal investigators say. These encounters suggest the bond that exists between loved ones is not erased by death.

"We don't know what to do with these stories. Some people say that they are proof that there's life after death," said Steve Volk, author of "Fringe-ology," a book on paranormal experiences such as telepathy, psychics and house hauntings.

Scientific research on crisis apparitions is scant, but theories abound.

One theory: A person in crisis -- someone who is critically ill or dying -- telepathically transmits an image of themselves to someone they have a close relationship with, but they're usually unaware they're sending a message.

Others suggest crisis apparitions are guardian angels sent to comfort the grieving. Another theory says it's all a trick of the brain -- that people in mourning unconsciously produce apparitions to console themselves after losing a loved one.

A telepathic link between loved ones

Whatever the source for these apparitions, they often leave people shaken.

Nor are apparitions limited to visions. The spirit of a dead person can communicate with a loved one through something as subtle as the sudden whiff of a favorite perfume, Volk says.

"Sometimes you just sense the presence of someone close to you, and it seemingly comes out of nowhere," Volk said. "And afterward, you find out that person was in some kind of crisis at the time of the vision."

Many people who don't even believe in ghosts still experience a mini-version of a crisis-apparition encounter, paranormal investigators say.

Did you ever hear a story of a mother who somehow knows before anyone told her that something awful has happened to her child? Have you ever met a set of twins who seem to be able to read each other's minds?

People who are extremely close develop a virtual telepathic link that exists in, and beyond, this world, said Jeff Belanger, a journalist who collected ghost stories for his book, "Our Haunted Lives: True Life Ghost Encounters."

"People have these experiences all the time," Belanger said. "There's an interconnectedness between people. Do you know how you're close to someone, and you just know they're sick or something is wrong?"

An eerie phone call at night

Simma Lieberman said she's experienced that ominous feeling and has never forgotten it -- though it took place more than 40 years ago.

Today, Lieberman is a workplace diversity consultant based in Albany, California. In the late 1960s though, she was a young woman in love.

Her boyfriend, Johnny, was a mellow hippie "who loved everybody," a guy so nice that friends called him a pushover, she said. She loved Johnny, and they purchased an apartment together and decided to marry.

Then one night, while Lieberman was at her mother's home in the Bronx, the phone rang and she answered. Johnny was on the line, sounding rushed and far away. Static crackled.

"I just want you to know that I love you, and I'll never be mean to anybody again," he said.

There was more static, and then the line went dead. Lieberman was left with just a dial tone.

She tried to call him back to no avail. When she awoke the next morning, an unsettled feeling came over her. She said it's hard to put into words, but she could no longer feel Johnny's presence.

Then she found out why.

"Several hours later, I got a call from his mother that he had been murdered the night before," she said.

Johnny was shot in the head as he sat in a car that night. Lieberman thinks Johnny somehow contacted her after his death -- a crisis apparition reaching out not through a vision or a whiff of perfume, but across telephone lines.

She's sorted through the alternatives over the years. Could he have called before or during his murder? Lieberman doesn't think so.

This was the era before cell phones. She said the murderer wasn't likely to let him use a pay phone, and he couldn't have called after he was shot because he died instantly.

Only years later, when she read an article about other static-filled calls people claimed to have received from beyond the grave, did it make sense, she said.

Johnny was calling to say goodbye.

"The whole thing was so bizarre," she said. "I could never understand it."

He had a 'whitish glow'

Josh Harris' experience baffled him as well. It involved his grandfather, Raymond Harris.

Josh was Raymond's first grandchild. They spent countless hours together fishing and doing yardwork in their hometown of Hackleburg, Alabama. You saw one, you saw the other.

Those days came to an end in 1997 when Raymond Harris was diagnosed with lung cancer. The doctors gave him weeks to live. Josh, 12 at the time, visited his grandfather's house one night to keep vigil as his "pa-pa" weakened, but his family ordered him to return home, about two miles away.

Josh said he was asleep on the couch in his home around 2 a.m. when he snapped awake. He looked up. His grandfather was standing over him.

"At first, it kind of took me by surprise," said Harris, a maintenance worker with a gravelly Southern accent. "I wondered why he was standing in the hallway and not in his house with everyone else."

His grandfather then spoke, Harris said.

"He just looked at me, smiled and said, 'Everything will be OK.' "

His grandfather then turned around and started walking toward the kitchen. Harris rose to follow but spun around when the phone rang. An aunt who was in another room answered.

"When I turned back around to look, he was gone," Harris said.

As if on cue, his aunt came out of the room crying, "Josh, your pa-pa is gone."

"No, he was just here," Harris told his aunt, insisting that his grandfather had just stopped by to say everything was OK. He said it took him a day to accept that his grandfather had died.

"Honestly, before that, I never believed in the paranormal," he said. "I thought it was all fake and made up. But I just woke up and I saw him. It couldn't be my mind playing a trick. He looked solid."

Fourteen years after his grandfather's death, there's another detail from that night that's still lodged in Harris' memory.

As he watched his grandfather walk to the kitchen, he said he noticed something unusual.

"It looked like there was a whitish glow around him."

'Can you come out and play?'

Childhood is supposed to be a time of innocence, a time when thoughts of death are far away. But crisis apparition stories aren't confined to adults and teens.

Donna Stewart was 6 years old and growing up in Coos Bay, Oregon. One of her best friends was Danny. One day, Danny had to go to the hospital to have his tonsils removed. Stewart played with him on the morning of the surgery before saying goodbye.

She said she was in her bedroom the next day when she looked up and saw Danny standing there. He wanted to know if she wanted to go out and play.

Stewart trotted to her mother's bedroom to ask her if she could play with Danny. Her mother froze.

"She went white," Stewart said. "She told me that wasn't possible."

Her mother broke the news. Danny had an allergic reaction during surgery and died, Stewart said.

"When I went back to my room, he was gone," she said.

Stewart, now an Oregon homemaker and a member of PSI of Oregon, a paranormal investigative team, said the encounter changed the way she looked at death.

"These experiences have made me believe that those we love are really not that far away at all and know when we are not doing as well as we could," she said. "Just as they did in life, they offer comfort during crisis.''

Still, Stewart often replays the encounter in her mind. She asks the same questions others who've had such encounters ask: Did my mind play tricks on me? Could he have been alive? Did it all really happen after he died?

De Santo, the former New Jersey hair salon owner, has taken the same self-inventory. The experience affected her so much she later joined the Eastern Pennsylvania Paranormal Society, which investigates the paranormal.

She said she checked with Michael's relatives and poured through a coroner's report to confirm the time of his death, which was put at Friday night -- almost 24 hours before she saw him at her salon on Saturday night.

She said Michael's body had been discovered by his cousin around 11 Saturday morning. Michael was slumped over his kitchen table, dead from a self-inflicted gunshot.

De Santo was baffled at first, but now she has a theory.

Michael started off as a customer, but she became his confidant. Once, after one of her pep talks, Michael told her, "You make me feel as if I can conquer the world."

Maybe Michael had to settle affairs in this world before he could move on to the next, De Santo said.

"A lot of times when a person dies tragically, there's a certain amount of guilt or turmoil," she said. "I don't think they leave this Earth. They stay here. I think he kind of felt he had unfinished business. He needed to say goodbye."

And so he did, she said. This is how she described their last conversation:

As they chatted face to face in the doorway of her shop, De Santo said they never touched, never even shook hands. But she didn't remember anything unusual about him -- no disembodied voice, no translucent body, no "I see dead people" vibe as in the movie "The Sixth Sense."

"I'm in a really good place now," she recalled him saying.

There were, however, two odd details she noticed at the time but couldn't put together until later, she said.

When she first opened the door to greet Michael, she said she felt an unsettling chill. Then she noticed his face -- it was grayish and pale.

And when she held the door open for him, he refused to come in. He just chatted before finally saying, "Thanks again, Nina."

Michael then smiled at her, turned and walked away into the winter's night.