Halsey shared the health update while announcing her fifth studio album and releasing its lead single, The End.
In it, she sings how "every couple of years now, the doctor says I'm sick".
The US singer-songwriter, whose real name is Ashley Nicolette Frangipane, is known for her track Closer with The Chainsmokers and her debut album, Badlands, which went platinum in the US.
"I told myself I’m giving myself two more years to be sick," she says in the Instagram video.
"When I'm 30, I’m having a rebirth and I’m not going to be sick.
"I’m going to look super hot and have lots of energy and get to redo my 20s in my 30s."
Halsey has spoken previously her poor health, saying: "I've kind of been sick most of my adult life".
But in 2022 she revealed her health became worse when she was pregnant with her son, Ender, the year before.
She's said she's been treated for conditions including endometriosis, Ehlers-Danlos syndromes, Sjogren's syndrome and mast cell activation syndrome.
She hinted she was now also being treated for lupus and leukaemia by tagging the Lupus Research Alliance as well as the Leukaemia and Lymphoma Society in her latest post.
One of the videos shared by Halsey show her receiving treatment in a hospital, and in her new song, she sings "poison" in her blood and starting treatment.
There are multiple types of leukaemia, which is a type of cancer that affects white blood cells.
The NHS says it's not known what causes leukaemia and the disease can leave patients more susceptible to infections and feeling run down.
It's normally treated with chemotherapy.
The other condition she hinted at, lupus, is complicated and poorly understood, according to the NHS, which says it affects many different parts of the body and can be life-threatening.
Selena Gomez has previously spoken her lupus diagnosis, which she says she needed a kidney transplant for in 2017.
There are some types of lupus that just affect skin, but the term is usually used to describe a more severe form of the condition - lupus erythematosus (SLE).
That affects many parts of the body, including the skin, joints and internal organs.
Lots of can have the condition for a long time without knowing before they get a sudden flare-up.
The symptoms include extreme tiredness, rashes (especially on the face, wrists and hands) and joint pain and swelling.
Even mild cases can be distressing and have a big impact on quality of life.
But the symptoms can be similar to more common conditions so it's often hard to diagnose.
After sharing her story online on Tuesday, fans were quick to offer Halsey support.
Her post was liked more than a million times and attracted thousands of comments.
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