What's it like to battle with a dozen people talking inside your head?

Aged 39 and married to Joel, Rachel says: “My life feels mostly awesome. I get stunned by it sometimes, all the little mosaic pieces. I still struggle a lot, and I’ve got a lot to understand about the things I go through. It’s not like I’m super-wise – but maybe, one day, I will be.”

Though her life has undergone a remarkable transition, the legacy of her troubled past remains: she hears voices in her head, more than a dozen of them, each with their own identity that she visualises in drawings – some benign, but some threatening.

Her voices are divided into two groups: the younger ones have a sense of personality, like a family. There is a three-year-old she calls Blue: “When I first started hearing her I had this image of an incredibly sad, frightened little girl in a dark room, not reaching out for anything; it was horrible to feel that I couldn’t comfort her. Now she’s more playful.” There’s also Elfie: “She’s pre-teen, really grumpy. Actually, that’s harsh; she’s angry. I don’t listen to her as much as the others, so I’ve probably got a part to play in that, and I’m trying to work on it.”

Then there are those voices she calls the Three and the Not Yets, which are more intrusive and scary. The Three speak among themselves, distant and powerful, describing what she is doing and the people around her. “They induce a sense of distrust and fear around me being in the world,” she says, then breaks off to describe a conversation they’re currently having about her. “Rachel is talking to Moya [the RT writer]; she shouldn’t have said that, why is she saying that, Moya’s going to hurt her.”

The Not Yets, so named because she didn’t want to talk about them in therapy, are more violent. “They tell me to do some pretty hideous things and are very explicit. They have been very frightening to me.”

Rachel's impression of the Not Yets and Blue

After three decades, more than 20 spells in hospital and several attempts to take her own life, Rachel has come to understand these voices not as symptoms of an illness, but as her mind’s response to the horrific, sustained sexual abuse she experienced outside of the family in her primary school years. She says: “I was lucky in that I was born to a mum and dad in a family with two older sisters and I was loved. But like many kids, I believed that this abuse was my fault, that I was making it happen, and that I couldn’t tell anyone about it. I was super-cute, super-lovely, and no one knew this sense of evil that I carried in me.”

Her trauma was compounded by the shapes she had to twist herself into afterwards in order to live a double life. “What happened left me with big emotions that had nowhere to go. I squished them down because if I had thought about them in my day-to-day world, I’d have been crushed. So it came out in metaphors: monsters, aliens, big conspiracies.”

Rachel became so good at hiding things that when her parents took her to see a psychologist, she described her as the most mentally healthy teenager she’d met. “But all the time I was wearing this mask, terrified of what was inside me.”

Rachel talks about her diagnosis of schizo-affective disorder in this week’s Horizon, which looks at the lives of three people who have been diagnosed with conditions that feature hearing voices, paranoia and hallucinations. It comes at a time when mental health has never had a higher public profile following Prince Harry’s revelations about the depression he suffered after the death of his mother, Diana.

Rachel says that medication – which she’s now free of – should not be the only treatment, as it is for many. She recalls being so sedated that at times she could barely function. “I realised how far I felt from my husband, and I wasn’t really living in the world.”

It was going to a “hearing voices” group that saved Rachel’s life. “I saw that they were real people who had grandkids, skills, artistic talents – and that helped me open up to the world, to be curious about other people and myself and find a sense of humanity again.” And instead of ignoring the voices, she began to acknowledge them and show them compassion.

So why speak out now? “Diagnoses like schizophrenia often get a bad press. I wanted to show that there are human faces behind these labels.

“The medication gave me some space at a point of desperation, but it obscured the need to look deeper and try to understand what was happening. Medication has its place, for some, but it should never be the end of the story. There is so much more to explore.”

Horizon: Why Did I Go Mad? Is on Tuesday 2 May at 9pm on BBC2