Ms Cooper, who has the autoimmune disease Crohn’s, said she was rushed to hospital 12 years ago and was told without major surgery she had only four days to live.
She weighed just seven stone, her eyesight was failing, her heart rate had plummeted, her arms were black and blue and she was fed through a feeding tube, the MP said.
“But it wasn’t the prospect of major surgery that upset me – it was what they said next,” she told the conference.
“‘Even if you survive Daisy, even if you recover, you will probably never be able to work again. Your Crohn’s disease is so aggressive, at most you’ll be able to maybe do one day a week but nothing too stressful.
“‘You’ll likely need surgery every five years or so. Here’s an information pack about the benefits you might be entitled to.'”
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Ed Davey arrives at conference on jet ski
Ms Cooper, 42, said she lay in her bed and sobbed for “17 hours straight” as she felt her world had “fallen apart” and that she would never be able to campaign again.
She added: “Hopefully though, you can see that the story ends well!
“As is the case with so many millions of people, the NHS didn’t just save my life, the people who make the NHS what it is, gave me my life back.”
She said she often wonders what is happening to people who are suffering the same symptoms now and questioned if they can even get a GP appointment, or if they have to wait a long time for a scan or are stuck in a hospital corridor.
But Sir Keir Starmer earlier this week said the NHS would not get any more funding without reforming as he laid out a 10-year plan to fix the health service.
Ms Cooper also told the conference one of the first conversations she had with Lib Dem leader Sir Ed Davey after she became his deputy in 2020, was how the party was close to not existing.
“It was quite sobering,” she said.
“He said to me: ‘Daisy, we both know we’ve only got 11 MPs. But – when you add up our majorities – do you know how few votes stand between us and extinction? It’s 69,664. If we lose just half of those votes to the Tories, we will be wiped out’.”
That conversation has been in the back of her mind every day since, she said.
But she revealed she had not told “a single living soul” until now because they did not want anyone to know “we were in survival mode”, especially after boundary changes meant they notionally only had eight seats.
“Eight seats between us having a parliamentary party – or extinction,” she added.
“But here’s a new number for you: our MPs now represent seven million people! In parliament, I can’t even walk to the toilet without bumping into a Lib Dem MP!”