Halsey Announces Lupus & T-Cell Disorder Diagnoses

Halsey's clearing the air on her health struggles -- saying she's been diagnosed with both Lupus and a rare T-cell disorder ... but she's on the mend and trying to get back onstage.

The singer-songwriter revealed the shocking news to her millions of social media followers Wednesday ... less than 24 hours after posting a vid to IG announcing her new song "The End" ... while saying she's lucky to be alive.

Watch ... Halsey posted video showing her talking about her afflictions -- adding she feels like an "old lady" with all her pain. She adds she's trying to relive her 20s in her 30s -- a version where she's not so sick.

Other clips show her masked up, receiving treatment before hopping back in the studio ... and even bawling her eyes out.

She expanded on the post Wednesday ... telling fans she's grateful for their support before launching into an explanation -- revealing her diagnoses. She says both are being managed or in remission despite a rocky beginning, but she will likely have them for the rest of her life.

Halsey adds she's so happy to have music as an outlet, and looks forward to getting back onstage and singing her heart out with packed audiences.

Lupus is an autoimmune disorder that causes pain and inflammation, and can even attack internal organs. Halsey says she also has a lymphoproliferative disorder which -- according to the National Institutes of Health -- causes people to make too many lymphocytes, a particular type of white blood cell.

Incredibly, Halsey appears to have finished up her last tour while fighting through the disease. She is releasing a new album soon too, but no tour is scheduled yet.