Isabella shared her health update on YouTube, discussing what she's been experiencing while undergoing chemotherapy for a medulloblastoma -- a rare malignant tumor located at the base of her brain. The 19-year-old says she's suffering some memory loss due to the meds she has to take.

She explained ... "I'm given this drug to protect my hearing and just because I have a reaction to it, they give me Ativan. And for some reason, this happened last time too, I can't remember a single thing about that day."

In her video, Isabella included footage from her latest hospital visit, where she was eating a sandwich that she didn't remember ordering. She says the medication is why she might have come off "loopy" in recent videos she's posted.

Memory loss aside, Isabella says she's feeling a lot better following her latest round of chemo ... noting she isn't experiencing much pain, and even slept about 18 hours after the treatment.

Isabella's chemo will end soon, and she admitted feeling a little scared ahead of the milestone -- "Once I'm done, how I'm gonna go back to normal life? ‘Cause I feel like there's always gonna be another treatment or something I have to do."

Isabella went public with her diagnosis in January 2024, sharing the news alongside her dad on "Good Morning America."