The 32-year-old, who shot to fame with her starring role in the latest "Star Wars" trilogy, has previously discussed struggles with endometriosis and polycystic ovaries.
But after filming the thriller "Magpie" in 2023, Ridley felt exceptionally fatigued and irritable, she told "Women's Health" in an article published Tuesday.
She said she initially dismissed her symptoms, which also included weight loss and hand tremors, to the role's intensity.
"I thought, 'Well, I've just played a really stressful role; presumably that's why I feel poorly," she said.
But discussing the symptoms with her doctor ultimately led to her being diagnosed with Graves' disease.
Graves' disease is the most common cause of hyperthyroidism, and is more likely to affect women than men, according to the European Thyroid Association.
Other celebrities to have suffered from it include rapper Missy Elliott and former US first lady Barbara Bush.
"We all read the stats about women being undiagnosed or underdiagnosed and sort of coming to terms with saying, 'I really, actually don't feel good,'" said Ridley.
Already a vegan, Ridley said she has switched to minimizing gluten intake since her diagnosis, among other lifestyle changes.
The last Star Wars trilogy ended in 2019 with "Episode IX: The Rise of Skywalker."
Since then, Disney has promised three new feature films about the sci-fi universe created by George Lucas, one of which is to star Daisy Ridley again as her character Rey.
