“Through my dread and my fear, I saw the beauty in them, the patterns in the universe. I could tell it was dangerous, this raw energy, this coursing feeling, and for a moment, I wished I could tumble in, tumble into the madness.”

Catherine Cho’s episode of postpartum psychosis came on when her baby was three months old. She and her husband James had taken Cato to America from their home in London to introduce him to his relatives. Everywhere they went, their Korean families told them off for defying the Korean custom of keeping the baby inside for the first 100 days and risking his health during the flu season. Cho took on their anxiety, doubting her own ability to cope. Then one day she saw Cato’s eyes as devils’ eyes. Within hours, she lost all sense of time, imagining herself as her own grandmother and her son’s child, and became convinced she was in hell and that her son was going to die as expiation for their sins. By the time she was sectioned, she had forgotten who she was.

Inferno is a brilliantly frightening memoir about Cho’s two weeks on the psychiatric ward, elegantly interwoven with tales from her past. We hear about her childhood, raised by Korean parents in an austerely silent American home, where Cho had to protect her brother from her father’s violent rages. We hear about her relationship with a near-murderous boyfriend, and then about her courtship with James, whose kindness promised to erase the past. There’s no easy cause and effect here, no suggestion that past trauma causes the psychotic breakdown. But the past experiences resonate, and in fleeing her vulnerable son Cho also flees her own vulnerable younger self.

Insights of this kind are rarely explicit. Cho’s language is poetically associative and points are made through suggestive juxtaposition. Fragmentary structures can feel merely fashionable, but here it feels hard won, allowing Cho to juxtapose everyday reportage about life in a psychiatric ward with more florid accounts of her psychosis. While Cho paces, expresses milk to alleviate her painful breasts, and writes frenetically in the notebook where she is reconstructing her memories, she observes the other inmates, many of whom have no homes to return to. She notices that it’s the race majority in the TV room who gets to be in charge of the remote control. And she learns the rules. As in prison, you never ask another resident why they are there.

Arguably, by the time Cho is observing this, she has ceased to be as ill as she was when admitted. Indeed, the intelligent curiosity with which she observes the ward becomes a crucial part of her recovery. Given the brevity of her psychological problems, she may not have much new to tell us about psychosis. But the real strength of the book is its revelations about motherhood and mental illness. Running through her psychosis is fear about herself as a mother. She fears for her baby and that she will forget she’s a mother altogether. These are common anxieties, and one of the book’s most compelling suggestions is that even ordinary motherhood resembles psychosis. The sense of being outside time, the terror of being responsible for another life, the feeling that the word “mother” defines us and yet remains dissociated from much of our mental life: these are familiar feelings, and yet Cho’s book reminds us how close they are to psychological illness, especially when you add in the immigrant’s feeling of living in parallel realities. Korean traditions and stories thread through the book, adding to the feeling that the reality Cho is now accustomed to – being a middle-class mother in Britain – is only another story, which might turn out to be as unreal as the fantastical folktales she’s grown up with.

In the end, Cho goes against Korean tradition by believing in love. “As for love,” she writes at one point, it is seen by her relatives as “an unfortunate passion, irrational and destructive”, partly because “any happiness must be bought with sorrow”. She comes to believe that it’s her love for James that takes her into psychosis, because her attachment to him becomes the site of her vulnerability, and that pulls her out again. Her love for Cato is more elusive – and among the book’s strengths is its bravery in admitting that the “fierce, possessive affection” she feels for her baby is very different from the kind of in‑love feeling she expected. When love fails, she has to remake her relationship with Cato. Part of what makes Inferno so moving is that we can feel her doing this as she writes, writing herself into motherhood and into a form of sanity that does not leave behind the insights enabled by psychosis.

• Lara Feigel’s Free Woman: Love, Liberation and Doris Lessing is published by Bloomsbury. Inferno by Catherine Cho is published by Bloomsbury (RRP £16.99). To order a copy go to guardianbookshop.com. Free UK p&p on all online orders over £15.