Jess Glynne has said anxiety led to her cancelling a performance at the Isle of Wight festival at the weekend, minutes before she was due to go on stage.
Writing on Instagram, Glynne said: "I got ready and was about to head to stage but I just couldn't do it. I was incredibly weak and full of anxiety."
"I can't help that my body sometimes gives up on me.
"I am so, so gutted, sorry and upset that I couldn't perform yesterday," she posted.
Glynne recently supported the Spice Girls on their UK tour.
"The last thing I ever want to do is let people down, I am sorry to anyone who I upset, it was not my intention."
Festival organisers tweeted on Sunday to explain Glynne was "physically exhausted".
The singer cancelled her performance at Radio 1's Big Weekend in Middlesbrough in May, hours before she was due to take the stage, after losing her voice.
There were reports of booing crowds as Radio 1 breakfast show host Greg James apologised for having to be "the bearer of bad news".
Some Twitter users who said they had bought tickets to see Glynne at this weekend's festival were unhappy with the last minute cancellation.
Exhaustion is working for the NHS doing 14 hours shifts! And on your weekend you rarely get off you go see someone you always wanted to, to be let down. Just saying— Cara louise butt (@caradeee) June 16, 2019
But Glynne said: "I had to do what was right for my physical and mental health. Kills me having to explain myself but I've just seen so much negativity online and in the press and it's so frustrating.
"I refuse to be made to feel like a bad person."
Glynne previously cancelled a performance at the Isle of Wight in 2015 to undergo throat surgery.
In 2018, her seventh number one single cemented her record for the most chart-toppers for a British woman in the UK.