Dr. Weiss stresses that he is a medical doctor who was not expecting to encounter past lives in a conventional therapeutic setting. (His favorite title, he says, is not “guru” but “professor.”) Under hypnosis, Catherine, the patient in his book, had memories of times and places, and in such extraordinary and historically accurate detail, he said, that she could never have invented them. (In one life she is an Egyptian servant in charge of embalming corpses. “I see eyes,” she told Dr. Weiss under hypnosis. “I see a woman, a goddess, with some type of a headpiece on ... Osiris ... Sirus ... something like that.”)

Critics of hypnotic regression dismiss such visions as scientifically dubious. “The mind fills in the blanks, basically,” said Dr. Jim Tucker, a child psychiatrist at the University of Virginia who studies accounts of past lives. “How are these visions different from dream material: that’s quite the question.” Nonetheless, Dr. Weiss’s elite credentials, and his initial skepticism, open the door to belief for people who might otherwise stay away.

“I’m not a big New Age person,” said a 47-year-old woman from Harlem who saw Dr. DeBell to cope with grief after her mother’s death. “I was really, really angry at the way my mother died. It’s almost as if I took it personally. How could this horrible thing have happened to my family? I’ve been such a good person.” (She declined to have her name published.) After two sessions of conventional talk therapy, Dr. DeBell hypnotized her and, she believes, led her to discover images of past lives. In one, she was an Italian merchant, a man, who sold textiles along the Amalfi Coast; in another, she was an African herbalist; in a third, she was a freed slave in New Orleans who healed the sick and ministered to those in need. This deep dive “was a tremendous help,” she said. It gave her a broader perspective on her life  and on the death of her mother: “I felt more at peace. My mother came, she did great things for me and she moved on.”

In a post-Freudian world, past-lives therapy has its advantages. For one thing, it’s quick. A regression session usually takes several hours  and costs more than $100 an hour. Under hypnosis, the patient follows a guided visualization. In his workshop in Rhinebeck, Dr. Weiss talked more than 200 people into a meditative state and then encouraged them to imagine walking through one of five doors. One had on it the year 1850, another 1700, another 1500 and so on. (All this reporter could visualize were Vermeer paintings; peasants in homey kitchens and the bourgeoisie at play.) “Any good therapist can use these techniques and you can learn them in a week,” Dr. Weiss said.

Whereas in classic psychoanalysis, patients used to have to see their doctors multiple times a week to talk about parents, childhood traumas and dreams, past-life therapists promise they can access the memories from which troubles stem in just one session. Catharsis and healing are nearly instantaneous results, Dr. Weiss said. “You don’t need six months of trust,” he explained. “This is the fast form.”