The former Girls Aloud singer has revealed she fell sick with mysterious symptoms, including tiredness and chest pains, but her doctor struggled to offer a diagnosis.

"You don't really notice it," she explained during an appearance on U.K. TV show Good Morning Britain. "You're like, 'I'm really tired. Is it with all the flying around, is it jet lag, am I getting sick, is it a cold, have we got a bug, why are we so tired all the time?'

"And then you would forget simple things. We couldn't remember the word for table, like, 'What is that? Put it on the...' We couldn't remember... It was the chest pains - I felt like I couldn't breathe.

"So I went to the doctors and I thought there was something seriously wrong, and they checked for everything and they said, 'You're fine', and I said, 'This still doesn't explain why I feel so bad'."

Nadine underwent a series of blood tests in a bid to find out what was wrong, and her doctor discovered she had been exposed to a gas, and she later discovered a faulty boiler at her home in Los Angeles had been spewing potentially deadly carbon monoxide fumes.

"Then when the blood tests came back they said it was exposure to high levels of gas, but still he hadn't said it was carbon monoxide... I thought, 'Is it London? Is it smog?' and then the guy in L.A. had seen that the boiler was faulty, there was a crack in it. It just happened to be someone was coming round - it was so lucky."

Nadine now hopes her experience with the toxic fumes will encourage others to get their boiler checked regularly and install carbon monoxide detectors.

"These (alarms) are crucially important - I have three of them now placed in different places. It's very, very scary and it's really serious."

Nadine is mother to a young daughter named Anaiya, who was born last year (14).