Why am I grieving a family member who is still alive?

I keep thinking of a family member who is still alive. But yet I am thinking far into the future to when I have to attend their wake and funeral. Sad music plays loudly in my head and I get very emotional. Because I this person is much older than me 39 years older than me to be exact and I think about their future passing. I do have Generalization Anixety Disorder along with Bipolar type 2 treated both with medication. I can vividly see these events even though I know they’re not real. And this family member currently doesn’t have any health problems. What might possibly be causing this?