The star had been due to sing the Australian national anthem for the Melbourne Cup at Flemington Racecourse, but she pulled out at the last minute and her backing singer, Nadia Aya, stepped up to take her place.

Jessica has now revealed an argument over her outfit broke out shortly before she was due to take to the stage, and she was struck down with crippling anxiety.

"It was the scariest moment ever. Before every performance, you need at least half an hour to focus on what you are about to do..." she tells "People think it's easy to get up there and perform one song but that one song is the hardest song to sing in Australia.

"Four minutes before I am about to be walked out from the green room, people on one side are bickering with people on another side and it started to suffocate me, it was crazy and I didn't know what to do... All I could feel was all the bad energy coming from people... It was really horrible..."

Jessica goes on to admit she was devastated to miss such an important performance: "I couldn't believe it was this gig. I know how to do the big gigs. I've done Eurovision, sung in front of Oprah (Winfrey), sung in front of (U.S. President Barack) Obama... But I didn't have a moment to refocus and pull myself back together and I am still in shock that it happened.

"I should have been prepared to just walk on stage and do my job, the job I love and they didn't allow me to do that... I was devastated, disappointed with myself that I couldn't find the courage to refocus with everything going on around me. I would never intentionally let anyone down."

She also credits her fans with helping her bounce back from the devastating moment, adding, "Their words of encouragement have meant everything to me."