Published Sunday, 02 February 2014
The singer, who won The X Factor in 2010, checked into London clinic The Priory on 29 December to reportedly tackle an addiction to prescription pills.
He subsequently cancelled a string of shows to focus on his recovery, and now he admits he was taking huge quantities of anti-anxiety drug Valium before his brother urged him to seek help over the Christmas holidays.
Cardle tells The Sun on Sunday: "I was so out of it - I was like a zombie. The doctor said to me if I'd been left to my own devices for another three or four weeks I might not be here now.
"I didn't have my wits about me to even count how many I'd taken. It was a lethal situation. Towards the end I was so out of it I was asking people around me how many pills they'd seen me eat.
"That is what kills people. It's what killed Heath Ledger and Anna Nicole Smith. Any time I started to feel stressed I would lean on the drugs and drink.
"I was kidding myself thinking I had a handle on it. That little word in front of the drug 'prescription' gave it an air of safety for me.
"But it's the total opposite - they are so highly addictive both physically and mentally."
The 30 year old is now gearing up to a UK tour in April and is determined to give fans his best as a thank you for their continued support.
He adds: "My fans have been so great - I just want to be able to go out and give it 150 per cent for them. I am completely sober for the first time in a long time - and I feel brilliant."