At the age of four, Lyndall Gordon did not go to nursery school like other children. Instead she became her mother's ‘sister’, learning what to do when she had one of her ‘attacks’.

She must fling water in Rhoda’s face when she collapses: “If she does not revive I must dig in her handbag for the large blue Mason Pearson hairbrush and push its bristles into her wrists. I never do this hard enough. Is this because I don’t have the strength or cannot bear to hurt her?”

The dramatic opening of Gordon’s memoir, Divided Lives: Dreams of a Mother and Daughter, describes how she saw her mother’s illnesses as a young child growing up in 1940s South Africa.

The daughter does not know what the illness is, nor does she understand how wrong it is for her father and grandmother to talk about Rhoda “giving way” and “needing to control herself”.

It is not until chapter five that readers learn the name of the illness — epilepsy. And Gordon herself, now an award-winning biographer, did not learn this until the age of 14, when she saw the word in one of her mother’s poems.

“Until that moment the problems besetting my mother seemed various: tension, fatigue, anxiety, falling, jerking awake, sleeplessness.”

Even then, she does not look up the word in a dictionary, but three years later ‘blurts’ the secret to a medical student boyfriend in Cape Town, Siamon Gordon, who tells her the diagnosis is probably correct.

“It could look like your mother is dying,” he says, but adds that she will eventually come round.

Lyndall married Siamon, and in 1976 followed him to Oxford, where he is now Emeritus Professor of Cellular Pathology.

By then she had escaped the intense relationship with her mother, and survived a mental breakdown in New York, followed by rescue in the form of a Rhodes Scholarship to St Hilda’s College.

She has spent the rest of her career as a tutor and lecturer in English at Oxford, combining her teaching with writing groundbreaking works on TS Eliot, Henry James, Virginia Woolf (this won the James Tait Black prize), Mary Wollestonecraft and Charlotte Bronte.

Her most recent biography, of US poet Emily Dickinson, was praised for offering a possible solution to the writer’s strange life — she shunned social contact and retreated to darkened rooms.

Gordon’s biography, Lives Like Loaded Guns, suggested that the mysterious illness which plagued her life could have been epilepsy.

She seems uniquely qualified to recognise the signs.

“I was already into the biography when I noticed she kept talking about ‘it’. It is not just the direct references — many of her poems are about a secret. Then there are the references to sickness: ‘I felt a Cleaving in my Mind/As if my Brain had split.’ She added: “I had grown up in a home where the word was never mentioned. It is still hard for me to mention it. It was not unusual that there was extreme secrecy about this illness, especially when it came to women. Caesar, Mohammed and Dostoevsky are all known to have had it, but their fame over-rode the stigma. When women had it, it could affect marriage.

“My father was only told about it the night before the marriage, which was not necessary as he wouldn’t have not married her, had he known.”

The author says of Emily Dickinson: “It would explain everything — the reclusiveness, the way she disappeared from parties. My mother was terribly fragile. It was difficult for her to go anywhere because you have only a few seconds warning.”

The most extraordinary moment in the memoir comes when Rhoda is told by her brother at the age of 31 that she has grand mal, the most severe form of epilepsy. It is a huge relief, because doctors have been treating her as a hysteric, and it releases her from “the obligation to control her illness by acts of will”. It also means that she finally accepts the medicines that can control the fits.

Reaction to the book — the Daily Telegraph described it as a ‘misery memoir with a twist’ — has made the author reflect.

“Perhaps most mothers would not reveal so much of their anguish. I was very conscious of my mother’s suffering —that was a word she used — I never thought she was making it up.”

The shape of the book was changed by her editor at Virago, Lennie Goodings. The author had intended to start with a paragraph describing South Africans’ feeling of colonial remoteness.

“I was not going to begin the book with my mother’s illness. She wanted to be a poet but decided not to publish because she felt so far away from the literary world. This feeling was reinforced by being a housewife — but also I wanted to get across how remote South Africa felt at that time.

“In today’s South Africa that is not supposed to be the case, but people do still talk obsessively about ‘overseas’.”

She spent several months re-writing after Goodings said she should put more of herself into the story. “I worked flat out from November to March, to put in more of my voice.

“It made me feel shy, so it was a bit different from some of my other writing.”

The memoir was partly sparked by the wish to recognise her mother’s talent as a poet, and as the inspiration for her daughter’s literary career.

“It was such a wonderful privilege to be read to by her — children’s literature and stories about children from Dickens, etc. She was a very charismatic person. Thoughts came off her in sparks. After the interest and stimulation of my mother, school was very dull and full of rules.”

Lyndall’s name marks her as “her mother’s creature” — it comes from Alive Schreiner’s novel The Story of an African Farm, about a woman “without a mask, rising from a bedrock of stone and bush”.

Rhoda’s progress as a poet ended partly because of lack of support from her husband, who ordered her home when she took a break in London to take poetry classes.

So does her daughter believe she might have been a published poet?

“I do. Her poetry is very good.”

Mother and daughter studied English alongside each other at Cape Town University. It was here that Lyndall was inspired by her mother’s intuitive reading of T S Eliot to start on the research that led to her into academia.

Her approach to literature through biography — and vice versa — was unfashionable at the time. English literature tended to focus on analysing the words on the page, without outside knowledge. And 20th-century biographies were often huge tomes in several volumes.

She feels vindicated by the current popularity of biographies that illuminate writers’ work by focusing on one aspect of their life.

“I do not believe that you can tell the whole truth about a life. There are always going to be gaps. You need some narrative thrust. I always ask ‘what story do you want to tell?’ There are as many stories as there are readers.”

The most distressing chapter of her memoir to write, she says, was the one describing the years in New York after she left South Africa — and separated from her mother, who had dreamed of her daughter starting a new life in the ‘Promised Land’ of Israel.

Instead, Lyndall had followed Siamon to New York, where, after giving birth to her oldest daughter Anna, she was diagnosed with post-partum depression. She now believes the crisis was partly because her mother’s illness had prevented normal teenage rebellion.

Rhoda flew in to look after Anna, urging her daughter ‘not to give way’. In one of the most moving episodes in the book, the author describes fleeing one day after receiving electro-convulsive therapy to “surprise Siamon at work” and tell him: “I can’t go on”.

In the book, she describes how he takes her hands and says: ‘First of all, you will get well.’ The book continues: “This is in character, he’s a maker of plans. ‘Do something with your life,’ he says, and he is quick with ideas — a doctorate for a start.

‘I’ve always thought you could write biography,’ he suggests. It is an offer to help me find a sense of purpose equal to his own, like the purpose my mother once nurtured for herself, a purpose it has never occurred to me that I warrant.”

The ‘sense of purpose’ coincided with the birth of women’s liberation, which meant that she was luckier than her mother. As one of the first female Rhodes Scholars in Oxford (an Act of Parliament was needed to change Cecil Rhodes’ will), she was offered her dream career.

Oxford was a steep learning curve, she says, since she needed to relearn English.

“I have come to England as a native speaker, but somehow unprepared for a language played out with so much grace and nuance, such extended diphthongs, such undercurrents of irony. Such ways with words reconfigure the brain.” And she loves the Oxford tutorial, which “seems continuous with a habit of sharing books that had been part of growing up”.

So what of the title — does she feel the book has anything to tell other mothers and daughters?

She feels that is up to the reader to decide: “My relationship with her was unusual because she said would I be her sister and I felt very honoured. I was allowed entrée into adult dreams and to some of her suffering. I think what is similar to other mothers and daughters is that there was an affinity. But my mother’s needs were very great.”

The book ends more calmly than it begins, with the author introducing her grandson Humphrey to the joys of literature: “Humphrey’s lips part, revealing his first tooth, as Peter Rabbit crunch-crunches on a carrot in Mr McGregor’s garden.”

* Divided Lives: Dreams of a Mother and Daughter is published by Virago at £20