Girl's Day's Hyeri revealed the real reason why she fainted on M! Countdown's January 16th episode.
On February 15th, she had a tell-all interview on MBC’s “Human Documentary.” On the interview, she recalled the moments
on that day. She said that she just remembered going up and performing
the first verse and chorus on stage, but she already forgot what came
after that.
She disclosed that the real reason of her loss of consciousness was due to the fact
that she contracted the H1N1 influenza. But she explained that she
didn't want to be limited from performing and expressed that she
believes that it's disrespectful to her fellow members and fans if she
wouldn't perform.