The screenwriter Abi Morgan, best known for the films The Iron Lady, Shame and Suffragette and more recently for the much-loved BBC series The Split, works in a small flat above a perfumery in Islington, north London. Its rooms, pale and sleekly minimalist, not only smell lovely, the rose geranium and vetiver floating obligingly upwards; they’re also, for a writer, extraordinarily tidy. The casual visitor would not think for a single moment of fraught commissioning meetings and hurtling deadlines were it not for the little squares of paper that line one wall, on which the episodes of her latest project are neatly summarised. But like everything about Morgan, this tranquility is, perhaps, deceptive. While she, too, exudes a warm, outward calm, her interest extending to everyone she meets, inwardly it’s a different story. Sometimes, it’s as if a bomb has gone off deep inside her. “I am both absolutely the same and profoundly changed,” she says, sitting at her white table, turning her white coffee cup in her hand.

Morgan is about to publish her first book, This Is Not a Pity Memoir, which tells the story of all that happened to her family between June 2018 and June 2021. It begins, as most stories of catastrophe and loss do, on a day like any other. On this morning, her now husband, the actor Jacob Krichefski, who has MS, doesn’t feel fantastic, but Abi, who’s tired and only wants to be able to drop their children at school and head to work, is unsympathetic: has he, she wants to know, taken a paracetamol? It’s a crotchety-ness – “you’re a bad nurse,” he says, just before she leaves – that she will soon come to regret. When she arrives home that afternoon, Jacob is lying on the bathroom floor, his lips blue, dried blood caked around his mouth. An ambulance is called and it’s blue lights all the way.

In hospital, Jacob has a series of seizures and his behaviour grows ever more strange and erratic, so strange and erratic, in fact, that he is soon transferred to the intensive therapy unit at London’s National Hospital for Neurology and Neurosurgery in Queen Square, one of the best neurological departments in the world. All the scans and tests keep coming back fine. Perhaps its experts can solve the mystery. But no. For the time being – it will be months before she learns that the withdrawal of a supposed wonder drug for MS, for which Jacob was part of a trial, has caused his collapse (he is one of just 22 patients to have suffered this catastrophic response) – the mystery continues and his condition worsens. Slipping in and out of consciousness, his body begins to shut down. The treatments the growing team of doctors around him try – he has been found to have a type of brain inflammation called anti-NDMA receptor encephalitis – fail to work. His blood pressure fluctuates, his breathing grows shallower. Finally, it is decided: Jacob must be put into an induced coma, a sleep from which he will not wake for seven months.

And when he does wake up, it’s not the end of the story. Another story is just beginning. For months, Jacob will be in rehab. In the end, he will spend 443 days in hospital. He will return home a changed man. Someone who needs round-the-clock care. Someone who doesn’t recognise the woman who has spent so long at his bedside, feeling terrified. Meanwhile, a bell is now “clanging” inside her, too. Something is wrong. She doesn’t feel right, either. In April 2019, soon after Jacob has emerged from his coma but while he is still in hospital, she is diagnosed with a rare and rapacious form of breast cancer. Her treatment for this – a mastectomy and chemotherapy – goes on into the autumn, even as she continues, as often as she is able, to drive to the hospital to see Jacob, and lasts until February 2020, by which time he is home, but the Covid-19 pandemic is about to land. This will make everything a good deal more complicated, for them as for everyone; it will also mean that when Jacob suffers a relapse – problems with his breathing – no one will be able to visit him in hospital.

***

Morgan doesn’t, to put it mildly, go in for self-pity. Her book, even when things are at their most bleak, is both very funny and as propulsive as a thriller, ticking along in an adrenalised real time, impossible to put down. But then, as she observes, in times of crisis it’s useful to be a writer. However huge her heart – her book, not without reason, is billed by its publisher as a love story – there’s no denying that it also contains an icy chip that makes pretty much everything fair game as material. “How do I feel about the book now?” she asks. “I feel that it’s like when you get really drunk and then the next day you wonder: what the hell did I say? I’d be lying if I told you that I hadn’t worried about invading Jacob’s privacy. My sister was its first reader, then my children, then Jacob’s family; I knew before I took it to any publisher they all had to be comfortable. But I’m also a dramatist and Jacob is an actor. We’re used to being fascinated not only with other people’s lives, but with – on the most narcissistic level, probably – our own, too.” After he’d woken from his coma, Jacob experienced, for a time, a delusion that Morgan was not his partner of three decades and the mother of his children, but an impostor: “When that happened I do remember thinking: this has got to earn its keep. It [writing] was almost in retaliation.”

What was it like, not to be recognised by him? “It was like a bad party game. There was something genuinely peculiar and creepy and terrifying about it. It really shook me; I was literally shaking. And having been rubbed out myself, I have a slight delusion now. ‘Is this real?’ I sometimes think [when I’m with Jacob]. ‘Are you really back? Do you know me?’” Was it lonely, living with him through this? “Oh, I had huge loneliness. It was only when he looked in the mirror and I saw that he didn’t recognise himself that I stopped feeling so alone. But I fought it. I was so indignant about it, so angry with the delusion, that I thought: screw you. I got very insane, trying to get him back. I would screw with him. I’d pinch him and poke him; I’d be annoying. I’d move things – I’d slide his porridge bowl to the other end of the table – as a way to get him to acknowledge me.”

If trauma is “unbelievably boring” in its relentlessness, it’s also, she believes, “incredibly stimulating”. But writing the book was more than a creative act; in so many ways, it was an anchor. “Primarily, I did it because I was losing my mind and I was trying to hold on to my sanity,” she says. “I was very, very frightened and I didn’t want my children to be frightened; I thought that if I could hold it all and write it down for them to read… that they might feel that [a book] was a safe place, as if it was over there, rather than here.” And then there was Jacob. Not only did she want to write down what he’d missed, all the stuff he would never remember. She longed to be able to talk to him. Writing was the best available substitute for conversation. “I wasn’t talking to the Jacob of now. I was talking to the Jacob before he collapsed. I was almost shouting into the cave, to hear what echoed back.” Whose story is it, really? She wrestles with this. “I grimace slightly when I see it called a love story. But it is. If it’s brutal, the person it’s most brutal about is me. When my daughter read it, she said, ‘Mum, are you OK with people not liking you?’ And there is a truth to that.”

But I can’t imagine, even for a minute, any reader taking against her. In person, she is intensely likable, the kind of woman you want to make your friend. I like her big, round spectacles and her denim shirt with its puff sleeves; I like her talk of batty diets and all the questions she asks me about my life (you’d tell her anything – and I do). And so it is on the page, too. She seems so lovable, without even trying, and so do her children and extended family. The couple have so much support, so many good friends. I’m ashamed to say that I felt (almost) envious. She pulls a face. “I say in the book that I fell in love with Jake’s dad before I fell in love with him. We have walked side by side in caring for him. But if it all sounds a bit Seven Brides for Seven Brothers… I’d want to punch someone in the face who sounded like that. There was a huge anger, too. I was very territorial over Jacob. I understood why widows throw themselves on to coffins, physically trying to hold on to somebody.” What about her children? They seem to have coped so well. “They were 14 and 16 when Jacob collapsed. They were on the edge of being cooked and I don’t know how we would have managed if they had been tiny. But yes, they were amazing running partners.”

***

She met Jacob at a party. She’d always vowed not to get involved with an actor, but there he was: they collided with “absolute velocity”. By their fifth date, he’d virtually moved in. Their relationship wasn’t without its complications – their daughter was a baby when they first had counselling – but she was also certain about him, this energetic, joy-chaser of a man. Her parents (her mother is the actor Pat England, her father the theatre director Gareth Morgan) divorced when she was small, though they remained friendly, and somehow this has worked in her favour. “I’ve always felt less, rather than more, likely to separate,” she says. “Though I am curious about the legacy of divorce, for children.”

She once said that her father’s decision to leave his marriage involved courage. Does she still feel this? “Yes, totally. It’s incredibly hard to leave a marriage.” This was one of the things she wanted to explore in The Split, a series based around two sisters and their mother, all of whom are divorce lawyers. “Divorce isn’t failure,” she says. “Some marriages are finite. We don’t all die of consumption at 40. We live long lives – too long, sometimes, to spend with one person. And marriage is changing. I got married to Jacob at a point when all the archetypal reasons for marriage are no longer there.” She laughs. “Marriage for me was a desire to adopt Jake.”

Ah, yes. Spoiler alert. Reader, she married him. This Is Not a Pity Memoir ends with Abi telling Jacob that she thinks they should do it at last, if only for tax reasons. But he’s not convinced. “Hmm,” he says, eating some pomelo, newly remembered as his favourite fruit. In the end, she has to bribe him. “There’ll be cake,” she tells him, at which point he agrees. So when did it happen? “Last June, at Wood Green register office,” she says. “A perfect, funny, lopsided, comical day. Twenty four people: just close family and friends. Then we went to our favourite restaurant, Luca [in Clerkenwell], and there were speeches. Jacob was very quiet all day. At that time, he didn’t communicate very much. But he was smiley and from then onwards, he has steadily improved. The past six months, that improvement has been radical. He’s zinging. He’s 80% of himself. He banks up his life with activity: his ukulele, football, musicals. We’re lucky. I have the wherewithal. A lot of therapies have been thrown at him, and we have a fantastic carer who comes in on half days, and a housekeeper in the afternoons, so there’s always someone around. I’ve got huge hope and ambition for him.”

Which parts of him have not returned? She thinks for a while. “I want to get this right. He has missed a profound experience. It’s like we’ve all been on a trip that he didn’t go on. So there’s that. He’s very happy. He’s sweet and funny. But he wants to be in the context of house and home. Psychiatric issues, emotional complexity, memory. Physically, he’s got bad balance. He can’t eat with his left hand. An interesting thing is that when a person has a brain injury, the body floods with calcium, to build the skull. These deposits have caused problems with movement on his left side.” Can she talk to him? “Our connection is really strong. Our friendship is back. Though it’s very recent that I can talk to him about a worry. His response will be thoughtful and genuine. But without… responsibility. He can’t drive the family forward.”

I loathe it when people talk earnestly of learning from terrible experiences. But I do wonder what the landscape of her life looks like now. “That’s a good question, actually,” she says. For her part, she thinks – because it is realistic to do so – only in five-year blocks. “I know who I want in my boat now and I know what I need to survive. When you think you’re going to lose the person that you love, when you think that you’re going to die yourself, it becomes very clear what you need to stay alive and you don’t need as much as you think. So my ambition is slightly different now.” In spite of everything, she has the uncommon energy of the middle-aged woman, the feeling that, in some ways, she’s only just getting started. “A producer friend was talking about the next 10 years and she said, ‘You need to work out what you want to write.’ I’ve been thinking about that a lot. Do I want to be known for something, rather than lots of things?” She would like to direct and wants to be behind the camera when This Is Not a Pity Memoir becomes, as she hopes it will, a film.

But really, what she has learned has mostly to do with love. “Let’s be honest. I’m a tufty-haired, one-breasted, fiftysomething woman who’s got a few Baftas and yes, that’s brilliant. But life also goes in cycles. I am not the big I-am. I think my greatest fear is to end up some old buffer at Bafta. Being with Jake, and what we went through as a family, has changed us. We have a greater appreciation of each other. We’ve seen each other at our worst moments. I didn’t realise I loved Jake so much – that’s the biggest revelation. It’s such a platitude, isn’t it, love? But… this hum. That’s the only way I can describe it. I just have this hum for Jake that I don’t have for anyone else.”

• This Is Not a Pity Memoir is published on 12 May by John Murray Press (£14.99). To support the Guardian and Observer order your copy at guardianbookshop.com. Delivery charges may apply

• On 11 May, a reading of extracts from This Is Not a Pity Memoir (by actor Fiona Button from The Split) plus a Q&A and signing in support of the National Brain Appeal will take place at the Royal Court Theatre, London SW1