Olivia Attwood was forced to withdraw from I’m A Celebrity… Get Me Out Of Here! after a routine blood test showed she was anaemic.
The test, which all the contestants undergo randomly throughout the show, also revealed low sodium and potassium levels, prompting staff to immediately take her to hospital.
The former Love Island contestant, 31, disclosed the reason for her departure after only 24 hours in the Australian jungle in an interview with the Mail On Sunday.
She said: “I was so scared, I was like: ‘What the hell is wrong with me?’
“They couldn’t give me an answer, they just told me that they had to get me to the hospital immediately.
“The results were really, really low when they put them into their reader and they consulted with another doctor off-site.
“I had those bloods done in England before I left, and they were fine. I was confused and of course very, very worried.”
However Attwood said that when the tests were repeated in hospital, they came back normal.
She was then taken to a hotel to sleep while ITV decided whether she could re-enter the camp.
She added: “They said because of the results the show’s medical team got from my readings, they were not happy to sign me off to come back in, even though I had the clean bill of health from the hospital.
“If I went back into camp, they feared my levels might drop and it could be detrimental to my health and wellbeing.”
She said ITV was not “willing to authorise my return and therefore I wasn’t insured”, before adding she was “absolutely devastated”.
On landing back in the UK she had more blood tests, which again came back fine.
Asked whether she will receive her full fee for the show, reported to be between £100,000 and £125,000, she replied: “We haven’t discussed that yet.”
Attwood also said she was not aware Matt Hancock was joining the show until she turned her phone on at Brisbane Airport on her way home.
She said: “It’s funny to see him slimed and gunked but it isn’t funny if you didn’t get to hold someone’s hand when they died while he was snogging someone in his office.
“NHS workers are protesting to get paid enough money to survive and he is out earning money in the jungle. That doesn’t seem right, does it?”
A show spokesman said: “As a precautionary measure, Olivia needed to leave the jungle to undergo some medical checks.
“Unfortunately, the medical team has advised it is not safe for Olivia to return to camp as there needs to be further investigation.
“She has been absolutely brilliant and she’ll be very much missed on the show.”
It comes after the public voted for former health secretary Hancock, 44, to take part in his fifth consecutive trial on I’m A Celebrity.
He will face the House of Horrors on Sunday and be tasked with navigating an “eerie house in the jungle” full of critters.
Ant McPartlin and Declan Donnelly announced the news at the end of Saturday night’s episode, prompting laughter from the contestants as well as supportive comments.
Hancock’s previous trials have seen him covered in treacle and feathers, trapped inside a cage partially submerged in water, and crawling through dark tunnels.
McPartlin and Donnelly also announced viewers can now vote on which campmate will become leader.
Saturday’s episode saw Hancock and his 23-year-old campmate Owen Warner, known as Romeo Nightingale in Hollyoaks, face a jungle-themed version of the game show Who Wants To Be A Millionaire? entitled Who Wants To Look Silly On Air?.
Learning he would be taking part, Hancock laughed and said: “That was the most predictable outcome. It’s called looking silly on air, it will be me then.”
All the campmates watched on as co-hosts McPartlin and Donnelly explained they would need to secure 11 stars to feed the entire camp.
The presenting duo then asked six multiple choice questions with 60 seconds to answer each, and the help of various lifelines.
Hancock and Warner were drenched in brown sauce before using the Ask The Hosts lifeline. McPartlin correctly answered who plays Sirius Black in the Harry Potter movies – Gary Oldman.
They failed to guess which Australian city the Hemsworth brothers were born in, while another question was halted after the campmates watching on tried to give away the correct answer by coughing loudly.
Hancock and Warner then called Sue Cleaver for help using their Phone A Friend lifetime, for a question that involved the year Coronation Street started.
The soap star was drenched while she took the call, with Warner shouting: “Leave Sue alone!”
I’m A Celebrity… Get Me Out Of Here! continues on STV at 9pm.