Olympic champion cyclist Elinor Barker has revealed the pain caused by endometriosis almost forced her to quit the sport.
The 24-year-old won Olympic, World, European and Commonwealth titles while suffering from the condition, which can cause pain, heavy periods and fatigue.
Barker says at times the pain was so bad she was unable to stand.
She had a successful operation last year, which she says "felt like I'd taken a weight jacket off".
"The first time I had really bad pain from it, I was in a friend's kitchen and I just fell on the floor instantly," she told BBC Sport Wales.
"But by the time I was there it didn't hurt any more. We were like 'oh, that was weird' and I carried on with my day.
"Then it just started happening more and more often, closer together until actually I felt like that for hours at a time and wouldn't be able to stand up.
"Which isn't much fun if you're trying to train or race at a World Championship level."
'Good days and bad days'
Endometriosis is a condition that affects around one in 10 women of reproductive age.
It is often difficult to spot as the symptoms are similar to other conditions and Barker says she went undiagnosed for years.
"Once I got diagnosed with it I was like 'great - this is a problem that I can solve'," says Barker. "Beforehand was really, really difficult.
"It was probably about a year and a half before Rio [2016 Olympics] that I started going to doctors and saying, 'look something's not quite right. I don't think most people are in this amount of pain'.
"It wasn't until just before the World Championships in 2018 that someone said 'oh actually it could be endometriosis'."
Barker says she had good days and bad days with the condition.
On the morning of the points race at the 2018 Commonwealth Games, Barker says she woke up pain-free and "knew I was going to win a bike race". She took the gold medal in style.
Australian swimmer Emily Seebohm also won gold at the Games. Barker said she heard the commentator say that Seebohm too had suffered from endometriosis and went on to read how the swimmer had had successful surgery to help the condition after becoming Olympic champion in 2016.
"I'm unbelievably glad I did go through the surgery," said Barker, who only missed five days of training as a result.
"I know it's not the kind of thing that goes away. So I'm not cured.
"It'll gradually come back over the next few years and I'll probably have to have surgery every three to four years if I want to live a healthy life and be training and racing."
'Difficult to have children'
The surgery helped Barker feel physically better but the condition has taken a mental toll too.
She was told last year it could be difficult for her to have children, something she is not ruling out in the future.
Barker says it was "a lot to take on board", as a then 23-year-old, and made her "question things in a way I hadn't really done before".
But despite almost quitting the sport, Barker says her love of cycling and the successful surgery kept her going.
And seeing the success of fellow cyclists Laura Kenny and Lizzie Deignan since they became mothers confirmed that she would look at starting a family when the time was right.
"I just thought I can't make decisions now based on how I'm going to feel ten years in the future," said Barker.
"I know that I love this and it makes me happy now so this is what I need to continue to do."
Barker is building up her training in Manchester as the Tokyo Olympics are just over a year away.
She will be hoping to have a pain-free build-up to a major championships for the first time in years.