Abuja - When 13-year-old Hoa was freed last month from a brothel in Guangdong, China, and brought back to Vietnam by her rescuers, her nightmare didn't end.
Traumatised and ill, she first returned to her village in North Vietnam's Nghe An province.
But there she lived in fear of being sold to traffickers again, and she was stigmatised by the local community for her four months in the brothel. She was later moved to a safe shelter in the capital Hanoi.
Like many former sex slaves, Hoa, who did not want to use her real name, suffers memory loss, depression, recurrent nightmares and an inability to concentrate.
She also finds it hard to trust people.
"Her mother loves her, but she doesn't know how to express her love. And it's hard for Hoa to believe her," said Chau Thi Minh Dinh, a psychologist at the Blue Dragon Children's Foundation, which rescued her, moved her to the Hanoi shelter and is helping her find a safe place to live.
There are almost 36 million slaves worldwide, according to the 2014 Global Slavery Index, published by the Walk Free Foundation this week. Many suffer extreme trauma, but there are limited resources to help them.
Thi Minh Dinh is the only psychologist at Blue Dragon, which has rescued 353 children since 2005, and she is one of the few psychologists in Vietnam who can help children like Hoa.
She telephones the most vulnerable every evening.
"At night-time they are scared, they are alone," she said in an interview.
They will need her support for many months to come, she said.
Pulling yourself together
How do the girls pick up the pieces after such a traumatic experience?
"It's better than you might think," said Michael Brosowski, director and founder of the Hanoi-based Blue Dragon Children's Foundation who, with Thi Minh Dinh, was speaking at the Trust Women conference in London on Wednesday.
"I think that young people have a resilience that is often difficult for us adults to understand, and in Vietnamese culture there is a real attitude of pull yourself back together again and get on with it. So those factors mean that the girls that we meet who have been rescued, they do surprisingly well."
Many recover enough to resume their studies, marry, have children and get jobs.
"But I think that underneath the surface there are always scars that remain," he added.
Stigma of counselling
It's not just people forced into sex work who are traumatised. People trafficked into other sectors, including domestic work, factories and the fishing industry also suffer extreme trauma and often suffer high levels of depression, said Cathy Zimmerman, who has researched the mental health of trafficking victims for many years.
"It's generally not a matter of move on, get over it... Generally people will need longer term support," Zimmerman, who works at the London School of Hygiene and Tropical Medicine, said on the sidelines of the Trust Women conference.
Zimmerman quoted a Lithuanian woman who had been trafficked to London: "I feel like they've taken my smile and I can never have it back."
How much care trafficking survivors need depends on what they have been through, their personality, and their situation once they have escaped.
People testifying in court against their traffickers may need more mental health support than "someone who is back in a comfy home with their family earning a nice income," Zimmerman said.
However, counselling is stigmatized in many cultures, and even if people are offered help, "they'll say 'no' because they think it means that they are crazy," Zimmerman said.
There needs to be a greater focus on finding out exactly what kind of assistance victims of trafficking need, she said.
"If you could find something that would work with a population that's as traumatised as this and as diverse as this . . . you could really roll that out to the millions of people who are being trafficked right now," she said.
"It's not just about prosecuting the perpetrators. In the end I think if you gave somebody the choice between regaining their mental health versus prosecuting their perpetrator, I think you know which one they'd choose."