Dr Barbara Lipska was working at her computer one morning in January 2015 when her right hand suddenly disappeared. Having spent her 40-year career studying the human brain, she immediately knew just how bad this was. The neuroscientist was aware that the most likely explanation was a tumour in the area of her brain governing vision. Having twice overcome cancer – in the breast in 2009 and then melanoma three years later – the spread of the disease was already a frightening possibility.

So when Lipska’s doctor called the following morning to report the results of an emergency MRI scan – three tumours in the brain, one of them bleeding, suggesting metastatic melanoma – she was undoubtedly devastated, but not completely surprised.

The prognosis was “effectively a death sentence”. At her age, then 63, and with that number of tumours, she knew she could expect to have between four and seven months. Instead, three years later, Lipska remains the director of the Human Brain Collection at the National Institute of Mental Health in Maryland, is training for a summer triathlon and has written an account of her experiences. She hopes this will raise awareness of an aspect of her illness about which, even with her extensive professional experience, she knew very little. “The idea that I might lose my mind didn’t enter my thoughts and was never discussed,” she says. “All anyone focused on was that I might die.”

Yet for two distressing months, after surgery and radiation and just as she began an immunotherapy clinical trial, Lipska slid into what she terms “insanity”, the tumours and swelling in the different areas of her brain triggering bewildering behaviour changes, lack of judgment, empathy and tolerance, and difficulty in relating to the world around her.

For some time her family did not realise these changes were an indication of what was happening physically in her brain. “I wasn’t a completely different person, more a caricature of my worst traits,” says Lipska. “There was always a vague link to reality. It could be excused away.”

When she summarily sacked a pest control worker, convinced of his intention to poison the household, alarm bells rang. Yet, reasoned those around Lipska, she was under a lot of stress, and of course the pest control chemicals were potentially toxic.

Lipska herself had no awareness of her tenuous grip on reality. “I was sure that everyone around me was acting wrongly. I thought they were conspiring against me, being mean.” The irony, she points out, is that she needed a part of her brain that was affected – the frontal cortex – in order to comprehend the very fact of it being affected.

When her brain was rescanned – her husband and adult children increasingly alarmed by her lack of empathy – 18 tumours were found. With the immunotherapy apparently initially unsuccessful, Lipska then began treatment with two drugs, trametinib and dabrafenib, newly available to patients with her type of melanoma. The “kitchen sink” of treatments began to work, shrinking the tumours. As Lipska’s ability to process emotions returned, the realisation of how unwell she had been was a difficult one.

“The most awful thing was that I hurt the people I love. As I regained my sanity, started coming back to life, I saw that I had no insight into my behaviour, I couldn’t recall the emotions. I learned that I upset my grandsons, who I love like nobody else,” she says, recounting an incident in which she shouted at them. “I feel terrible guilt even now. For me and my family this was such a distressing part of my illness.” Yet for the doctors treating the disease that almost killed her, any resulting mental illness was – understandably, she accepts – not a priority. “The concern was the cancer, the treatment of the tumours. What happened to me mentally was almost dismissed. Even afterwards, oncologists were never curious about it.”

As medical science advances, there are more survivors and medicine becomes ever more compartmentalised – “no one can specialise in everything” – but mental illness, she fears, risks being marginalised further. “I am a success story,” she adds, “a rare case. Not many survive my condition and are able to tell the tale afterwards. But if I had but lost my mind for ever, if the tumour had already ravaged the frontal cortex of my brain, if I had remained that monster and my family had had to live with that, would that be a success for me? I don’t know.”

Lipska has dedicated her career to understanding the mechanisms of mental illness – focusing particularly on schizophrenia – and her own survival affords her a valuable new case study. “I hope that my insight into living in a world which makes no sense can help advocate for people who experience mental illness for all sorts of reasons,” she says.

Most important, she states, is to build the understanding that mental illness is a disease of the brain and must be studied and treated as such, “just as coronary illness is a disease of the heart”. Notions of mental illness as different – “somehow involving blame” – still linger, she believes. “We are so far away from understanding how the brain functions. Understanding how it malfunctions is even further away. There is so much work to do.”

At her most recent scan, in January, doctors discovered another small tumour. She has just completed a course of radiation. It was a “heartbreaking” discovery, but one she and her family hope is “just another bump on the road”. In June she is aiming to complete a half ironman triathlon with her family. As they did at the same event last summer, Lipska’s son will cycle, her son-in-law will run and she will swim with a guide. “It is an incredible, bonding experience, however slow I am now,” she laughs.

Lipska’s illness has permanently changed her. She is blind in one eye, considerably weaker and she no longer fully trusts her mind. “My attitude to my brain and mental health has changed. I no longer feel invincible.” She is, she suspects, a “more feeling” scientist and a more tolerant person. When brains arrive at her lab, ready for research, Lipska and her team are simply given an age and a cause of death. “It could have been me. I look at them and I know each one holds so much personal history.”

The Neuroscientist Who Lost Her Mind: A Memoir of Madness and Recovery by Barbara K Lipska is published by Bantam Press (£16.99).