Scottish singer Lewis Capaldi has cancelled all of his live shows "for the foreseeable future", including his Australian tour, due to the impact Tourette syndrome is having on him.
His announcement came just days after he appeared to experience involuntary muscle movements and lose his voice , prompting the crowd to help him finish a song.
The 26-year-old, who revealed last September he had been diagnosed with Tourette syndrome, had taken a break from live shows before the festival.
"I used to be able to enjoy every second of shows like this and I'd hoped three weeks away would sort me out," he wrote on social media on Tuesday.
"But the truth is I'm still learning to adjust to the impact of my Tourette's and on Saturday, it became obvious that I need to spend much more time getting my mental health and physical health in order, so I can keep doing everything I love for a long time to come."
What is Tourette syndrome?
Tourette syndrome is a condition characterised by rapid, repetitive, involuntary motor movements or vocalisations, also known as tics.
There are two categories of tics: simple and complex.
"Simple motor tics would be a head nod, or blink, or a shake of the head and hand movements or scrunching your toes, and then you've got complex movements, which could be anything, really - could be even dancing," Tourette Syndrome Association of Australia president Mandy Maysey told SBS News.
"Simple vocal tics are grunting, sniffing, and things like that, and the more complex ones would involve words."
While complex vocal and motor tics can also include inappropriate language, or inappropriate gestures and touching - known respectively as coprolalia and copropraxia - they are not common, she said.
At least one in every 100 people have Tourette syndrome, Ms Maysey said.
Associate Professor Daryl Efron, a paediatrician at the Royal Children's Hospital Melbourne and the Murdoch Children's Research Institute, said Tourette syndrome was more commonly diagnosed in boys than girls.
"It usually starts in early primary school," he told SBS News.
"The pre-pubertal period is typically the worst period, although not always, and it usually gets much better through the teenage years.
"It still can happen in adults, of course, but it's much less common."
What causes Tourette syndrome?
Associate Professor Efron said while the exact cause of Tourette syndrome isn't known, there were "some genetic factors operating".
Ms Maysey, who has three children with Tourette syndrome, said research suggests people who have a family member with the condition are much more likely to have it themselves.
"You're either predisposed to it, or you're not," she said.
Associate Professor Efron said it was "unusual" for someone to only have Tourette syndrome, especially if it was severe.
"The kids that I see, they've almost always got other difficulties, like anxiety; ADHD; if not OCD, then obsessive-compulsive behaviours; learning difficulties are more common; autism spectrum disorder is more common, depression is more common — so a whole range of developmental and mental health problems," he said.
What impact can Tourette syndrome have on people's lives?
Associate Professor Efron said the "unpredictable, waxing and waning course" of symptoms can make Tourette syndrome a "very frustrating condition".
"Almost every person with Tourette syndrome has periods where their tics are less problematic, and then periods where they’re more problematic," he said.
"With kids, the periods where it's worse can be for a predictable reason - starting a new school year or something stressful is happening in the child's life - but quite often they'll get worse for no obvious reason."
Ms Maysey said "any kind of heightened emotion" could cause "an upswing in tics".
"So if you are super stressed, you will tic more; if you are really happy, you will tic more; if you're really excited, you will tic more," she said.
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Capaldi has previously said he's experienced severe bouts of anxiety and panic attacks.
Ms Maysey said having a co-existing mental health condition, like anxiety, could cause tics to become more debilitating, creating "a chicken and egg situation".
"There's every likelihood that Lewis is dealing with so much more than just what people are seeing up on the stage - he's not just embarrassed (he's experiencing tics), he's going to be massively anxious," she said.
"The more anxious he gets, the more he's going to tic; the more he tics, the more anxious he's going to get."
The unpredictable nature of tics can have a significant impact on the professional and personal lives of those with Tourette syndrome, Ms Maysey said.
"You don't know on any given day how it's going to affect you," she said.
"There are a lot of people out there with Tourette syndrome that cannot work certain jobs just because of the stigma, or just how it affects their daily lives, and there are times when people with Tourette's have just gotta say, 'Today is not my day, and I'm going to stay home'."
Can Tourette syndrome be treated?
Associate Professor Efron said "at the moment, we don't have very good treatments" available for Tourette syndrome.
"The tics … they're really difficult to treat. It's a combination of behavioural interventions and medications, but neither of them are that effective," he said.
"Often we're treating the other associated problems like anxiety, ADHD, learning difficulties, and so on, because those ones have got, probably, more effective treatments, so all those things are important to help a child with their overall function, school function, social life, self-esteem."
Ms Maysey said having a "really high level of concentration" on something could help to reduce people's tics.
"It's quite interesting that Lewis is ticking when he's singing, because usually, when you're doing something you really love and that you're really, really hyper-focused on, you just don't tic in the same way."
Being in nature could also help, Ms Maysey said.
"It's about just getting away from the frenetic … so anything that is going to relax the body and put you in a calm state is going to reduce your tics."
