Stephen Sutton has been re-admitted to hospital days after celebrating raising more than £3 million for a cancer charity.
The 19-year-old todaytold supporters on Facebook he was back in hospital after developing "breathing difficulties" on Saturday night.
The 19-year-old has collected more than £3.22 million for the Teenage Cancer Trust since posting a picture of himself in hospital in April with a goodbye message when he believed he was at death's door.
However, the inspirational young man made what he described as "a miraculous recovery", coughing up a tumour, and after successful surgery was well enough to be discharged from Birmingham's Queen Elizabeth Hospital on May 2.
But commenting today on his Facebook page - which has 750,000 likes - he told supporters he was again posting from his hospital bed.
He said: "Unfortunately today I've ended up back in hospital. I had some breathing difficulties starting last night and after going to A&E have been admitted back to a ward for monitoring.
"I've still got the cough, then quite quickly developed a wheeze in my breathing and breathlessness upon any physical exertion.
"There's no immediate panic and I'm currently quite stable - I have been put on nebulisers and other meds which are currently helping my symptoms hugely."
He added: "The doctors think there may be something restricting my airway again, they're not sure exactly what yet though (tumour regrowth, infection, inflammation, are all potential reasons mentioned), but are currently discussing the possibilities and my scan results to decide what to do next."
Over the weekend, a petition at change.org calling for Sutton to be knighted both for his charity work and efforts to raise awareness about cancer had attracted 31,300 signatures.
Sutton good-humouredly described his re-admission to hospital as "very inconvenient".
"I had a few cool things planned to attend today, then tomorrow was due to appear on the telly on BBC Breakfast News," he added.
"I understand my health is the obvious priority though and have had to cancel.
"Fingers crossed the issue will be resolved and that I'll be out of hospital soon - I'll keep you all updated with how I'm getting on."
The teenager, who is from Burntwood in Staffordshire, was diagnosed with bowel cancer when he was 15. Despite treatment the tumours spread, with doctors telling him the disease was terminal in 2012.
His story has attracted support from celebrities including comedians Jason Manford, Russell Brand and Stephen Fry, and the music mogul Simon Cowell.
He had been working through a 46-point bucket-list but recently said it had "now taken a bit of a back seat" so he could concentrate on helping and motivating others.
The teenager recently led a successful attempt to break the world record for the number of people making a heart-shaped hand gesture, setting a new benchmark of 554.