On Sunday evening, Robbie Williams performed to thousands of adoring fans – something he thought he might not ever get the opportunity to do again, he admitted.

The British superstar opened up about his health battle with agoraphobia, admitting it left him unable to get off the sofa for three years from 2006 until 2009.

Williams told  The Sun  he was sofa-ridden and couldn’t leave his home or continue to perform or  work because his mind told him he “shouldn’t go anywhere”.

“My career had gone stratospheric and taken me to Mars, and I needed some time to get my equilibrium back and get myself back together,” the singer candidly revealed.

“It was my body and mind telling me I shouldn’t go anywhere, that I couldn’t do anything. It was telling me to just wait — so I literally just sat and waited.

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“I was agoraphobic from around 2006 to 2009. Those years were just spent wearing a cashmere kaftan, eating Kettle Chips, growing a beard and staying in.

“I remember they offered me £15 million ($A26 million) to take over from Simon Cowell on  American Idol, plus a big gig in the States, but I turned it down because I wasn’t leaving the sofa at the time. I just couldn’t.”

Agoraphobia is a type of anxiety disorder where an  individual can  fear and avoid places or situations that might cause them  to panic and make them feel trapped, helpless or embarrassed.

Thankfully, the singer decided to get the help he needed when he heard the song  Human  by fellow musicians  The Killers  on the radio.

​“I remember listening to that Killers song and something in that moment made me think, ‘I had better get my a**e in gear, put an album together and tour’.​

Robbie eventually made a comeback on  The X Factor  in 2009 where he performed his  song  Bodies.

However the the appearance did not go as smoothly as planned when the sliding stage doors got stuck and a critic slammed Robbie’s “wide-eyed, unblinking and sweaty”  rendition was  a sign he “wasn’t the superstar he used to be.”

“There was no rhyme or reason why five minutes before that, it hadn’t happened. But when I did come back, it felt so unnatural. It’s why that Bodies performance was so bad — I didn’t know what the f*** I was doing, it didn’t seem natural to me any more.

“I had to re-learn how to entertain. It wasn’t an easy process — it was like having a car crash and then learning how to walk again.

The British star eventually re-joined the  Take That  tour in 2011, which broke all previous records for ticket sales, and extra dates were added to adhere to demands.

“If it wasn’t for Take That, and re-joining them, I don’t know if I’d have come back at all.”

He added,  “Initially, I got to hide in plain sight – I could hide behind my boys. They helped an awful lot.”