In the vid, shared to Tay's X account, the rapper is hooked up to a series of hospital machines, resting after what her account describes as surgery on a heart tumor.

It's a short clip, and she's knocked out through all of it ... but, her team says they're "overjoyed to share that Tay’s open-heart surgery was a great success" -- adding their deepest thanks to all of her doctors.

The account immediately followed up that post with another ... one in which the admins reference a death hoax last year they say was perpetrated by Tay's father, Christopher Hope -- and, add this isn't a hoax.

In case you don't remember ... last year news of Lil Tay's death went viral -- and, we broke the story that the news wasn't true. Lil Tay came out and blamed her dad for making up the rumor at the time, something he flatly denied.

It was hard to tell exactly who was telling the truth in that saga. What we do know -- many online aren't buying that Tay had heart surgery because of last year's saga.

It certainly appears more authentic now ... though it may not change the minds of some who are pointing out Tay has a new single coming out next week and think this might be a publicity stunt.

The person running her social media is clearly calling BS on that ... but, the situation's leaving fans scratching their heads once again.