The then 16-year-old was experiencing back to back periods and guessed something was not right with her menstrual cycle.
"I remember curling up on the ground and crying one day, and my brother who was at med school at the time saying, you really should look in to endo, because you tick a lot of the boxes," Watson said.
Two weeks after calling Endometriosis New Zealand, she got an appointment with a specialist and another two weeks after underwent surgery - the only way to definitively diagnose the disease.
Endometriosis affects one in 10 women in New Zealand. Its symptoms include period pain, pelvic pain, and sub-fertility or infertility.
It occurs when tissue similar to the lining of the uterus, grows in places outside the uterus. Laparoscopic surgery is the only way to definitively diagnose the disease.
Watson has since had a second surgery to remove endometrial tissue and said she had gotten better at managing it.
"Running sort of seems to ease to pain for me and I'm not sure whether that's because I'm thinking about the pain in my legs, or how hard running is, but that seems to be one way that I can quite effectively manage my symptoms."
While she was diagnosed quickly, Watson recognised many others were not as lucky and so she wanted to raise awareness to help change that.
Her main goal was to bring understanding on how the disease affected people and normalise talking about period problems.
Although, it is not the first time Watson has undertaken a big physical journey for this cause.
In 2020, for her 21st birthday, she kayaked 100 kilometres in a day by doing 10 10-kilometre laps of the Avon River and raised $4300 for the national endometriosis organisation.
On Hazza's Run for Endo, she will run and cycle more than 650 kilometres down the West Coast of the South Island while raising funds.
She began Hazza's Run for Endo on the Puponga Green Hills route in Farewell Spit on 2 December and plans to reach Ross by 9 December, her 23rd birthday.
She will run the Heaphy, Old Ghost Road and Paparoa tracks and cycle between them, then finish off by biking the West Coast Wilderness Trail.
"When I set the mission, it had to be something big enough to scare me and I've done big 50 kilometre runs but to do 85 kilometres [in one day] is definitely some unknown territory," Watson said.
"So I'm excited about the challenge and to see how far I can really push myself."
Her employer ANZCO Foods has sponsored the costs of her trip and has been supportive of her.
