Psychologist Edith (Edie) Eger is one of the few living Holocaust survivors.
After a happy childhood in Hungary, the Nazis sent her family to Auschwitz in 1944 when she was 16.
There she endured the death camps, the death march and was forced to dance for the infamous Josef Mengele.
Her parents did not survive. She and her sister did, but only just. When American troops liberated the camps in 1945 they found Edie barely alive in a pile of corpses.
After decades struggling with survivor's guilt, Edie - who lives in California - now helps people overcome victimhood and rediscover the joy and self-love she says we are all born with.
Edie's PTSD means she is still frightened of anger and loud speaking, she says.
"I go and drive somewhere, I see barbed wire, immediately I'm back in Auschwitz. You see, I never forget or even come to terms with it but I somehow found a way to go through the valley of the shadow of death, but not camp there or set up house there."
As a psychologist, she specialises in treating PTSD sufferers, and it was the realisation that she couldn't take people further than she had been herself that prompted her return to Auschwitz.
"I needed to go back to that lion's den and look at the lion in the face and reclaim my innocence and begin to forgive myself that I survived."
Edie wanted to honour her mother, whose words in the cattle car kept her spirit alive at Auschwitz.
"We don't know where we're going. Just remember no-one can take away from you what you put in your own mind," her mother said.
For many years after the war, Edie struggled with survivor's shame.
"I didn't need a Nazi, I had one in me."
She now likes to think of herself a 'guide', helping people get from victimisation to empowerment.
The title of her memoir The Choice reflects Edie's belief that, looking inward, we can find that we all have choices.
"The more choices we have, the less we feel like a victim. I was victimised, but I'm not a victim. It's not who I am, it's what was done to me."
At Auschwitz, Edie saw those who were too dependent on others were the first to die, some for no apparent physiological reason.
The best thing parents can do for children is prepare them to live independently, as dependency can breed depression, she says.
"Most people are hungry in their soul, and no food and no money and no things will ever, ever fill that hole in the spirit, in the soul.
"Depression many times is unresolved grief, and you don't medicate grief. You have a broken heart and you cry and cry until you can't cry anymore."
Expression is the opposite of depression.
"What comes out of your body doesn't make you ill, what stays in there does."
People who move beyond 'me me me' and commit to something other than themselves are much happier, she says.
To handle difficult feelings you have to stop running from them and instead face and embrace them.
"I feel that feeling and then I release it … I sit down and I say 'I have a feeling. There is no right feeling or wrong feeling, there is my feeling'. I give myself permission, I legitimise that feeling, and then I decide how long will I hold on to it. I take charge.
"It's only a feeling. You've survived it in the past, it happened to you in the past, and it will happen to you again because we are human.
"When you have a feeling, don't do anything but take a deep breath and see that no one really is making you angry, you're angry because your expectations are not met."
Revenge may give satisfaction, but it's forgiveness that leads to ultimate freedom.
"I am not allowing anyone to take residence in my body and [make me] a hostage or a prisoner of the past.
"No-one can make me angry or feel anything because I am in charge of my feelings, my thoughts and my behaviour."
"Just turn the hate into pity and feel sorry for people who do not really experience the beauty that God has given us, to live a full life and form a human family."
Edie has scoliosis and needs some help to function, but at 90 she feels younger than she did 60 years ago.
"I don't take any medications, I don't drink, I don't smoke, I go dancing once a week, swing dancing … I have three great grandsons, which is my best revenge to Hitler."
Edith Eger has written a memoir The Choice published by Simon and Schuster