Lib Dem deputy leader Daisy Cooper has told her party's conference how doctors warned her that, without major surgery, she would only have four days left to live.
The St Albans MP said her Crohn's disease was so aggressive her weight dropped to seven stone and she was warned she may never work again.
"I lay in my bed and sobbed. I sobbed and sobbed and sobbed for 17 hours straight. I felt like my world had fallen apart," she said.
She told the conference that the NHS had saved her life but that she feared for anyone going through the experience today.
"Can they even get an appointment with their GP? How long have they been waiting for a scan? Are they stuck in a hospital corridor - rather than a ward - as they scream with pain?"
She accused the previous Conservative government of having brought the NHS "to its knees".
She promised the Lib Dems would work with the Labour government and addressing the health secretary directly said: "Wes [Streeting], if you are listening - take up our ideas or put your own forward.
"If we don't see the right level of ambition or urgency, we will hold your feet to the fire.
"We Lib Dems must continue to campaign to save our NHS and care like our lives depend on it. Because I know, and we know, that so many people’s lives really do."
Recounting her own experience, Cooper told the conference in Brighton that 12 years ago she had been rushed to hospital.
"My weight had dropped to around seven stone. My eyesight was failing. My heart rate had plummeted. And my arms were black and blue. I was fed only through a feeding tube."
She said the NHS had not only saved her life but "gave me life back" adding: "Thanks to them, I got my strength back. Put on some weight. And decided to embrace my new life."
Crohn's disease and ulcerative colitis are forms of inflammatory bowel disease (IBD), which cause the immune system to go into overdrive and attack healthy tissue in the gut.
The conditions, which affect around half a million people in the UK, are life long and there is no known cure. Common symptoms of Crohn's disease include diarrhoea, stomach aches and blood in your poo.
Cooper also used her speech to celebrate the Liberal Democrats' success in the July general election, when the party won 72 seats, its highest tally since 1923.
Beginning her address with a triumphant "we did it", she went on to share with the audience her past fears that the party faced potential extinction.
She recalled a conversation she had in 2020, in which party leader Sir Ed Davey had told her the Lib Dems could be wiped out if it lost half their votes to the Conservatives.
She said the party had been in "survival mode".
But now, she said that, following their strong election performance, "I can’t even walk to the toilet without bumping into a Lib Dem MP."
Turning to the future, she the party would use its increased power in Parliament to champion its "top priority" of improving health and social care.
Over the weekend Sir Ed said the government had to "invest more in the NHS or accept continued decline".
The party has estimated the NHS needs £3.7bn a year extra in day-to-day spending and a further £1.1bn a year for investment.
It says it would pay for the £1.1bn for investment from borrowing, while the £3.7bn would be raised through closing loopholes in capital gains tax.