The 21-year-old, who is rumoured to be dating actress Ruby Rose, was misdiagnosed several times before doctors discovered she has the condition that causes inflammation outside of the uterus, pelvic pain, fatigue, nausea, and possible infertility.

"Emotional moment; but if any of you suffer from endometriosis please know you aren't alone," she writes on "I know how excruciating painful it can be and how discouraging the disease can be.

"To feel like it's going to limit you because of how debilitating it is. To miss school and work, or even worse to GO and suffer through it anyway feeling like a prisoner in your own body. To maybe be worried about 'never having kids' or dealing with crazy treatment suggestions.

"I was recently diagnosed after years of suffering and finding myself doubled over backstage in the middle of my sets, or fighting back tears on an airplane, or even being in so much pain I vomit or faint."

Halsey, real name Ashley Nicolette Frangipane, admits she was initially relieved when doctors correctly diagnosed her with the condition after years of telling her she was "being a big baby".

"Finding out that I had Endo was the most bittersweet moment, because it meant I wasn't crazy! I wasn't a 'baby'! I had every right to be feeling like the world was caving in. But it was terrifying to find out."

The Ghost singer is now offering to help other women struggling with endometriosis, adding, "Just know I'm here if you want to vent. I have managed to live a wild, incredible, and unpredictable life with Endo, and I'm here for you!"