The former Coronation Street star and TV presenter dances with Graziano Di Prima in the BBC One show and has revealed she suffered a panic attack in rehearsals that came "out of nowhere".
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Marsh, 46, told The Sun how she had always suffered from panic attacks, but hadn't suffered one in a while until it happened during training.
She said: “Everyone thinks that because you’re on the telly you must be amazingly confident, but the truth is that I’m not always and this is how that comes out.
“I don’t know exactly what caused it, I think I’d had some harsh comments from the judges the week before, I’ve been working other jobs at the same time too, so it’s tiring, and I just lost my confidence completely.
"I went to pieces and said ‘I don’t think I can do this’. At that moment I wasn’t sure I could even carry on with the show."
However, Marsh, who first found fame with Hear'Say after appearing on Popstars, said that the cast and crew pulled together to help her regain control.
She told how competitor Hamza Yassin had reminded her "we're only dancing" and said that her dance partner, pro Di Prima is "the most incredible man" who joins her family for dinner at home once a week.
Marsh explained that she has had therapy for anxiety, but still finds herself occasionally affected by panic attacks.
She said that her recent one had left her in tears and meant that she had to cancel the rehearsal.
However, Marsh is due back in the ballroom tonight, where she and Di Prima will dance an American Smooth in the live show.
Strictly Come Dancing continues tonight at 6.55pm on BBC One.
Watch: Kym Marsh says 'I've had impostor syndrome all my life'