Jay 🥀 • my guilty pleasure is listening to "if we were a movie" by Hannah Montana

I've struggled with anxiety for a major portion of my life, but have recovered greatly in my opinion. Sometimes it gets bad but nowhere near what it was before. Currently I keep having the intrusive thought (not a feeling but it kind of is??) that my young sister is going to die. It shames me and causes me so much anxiety. I love her more than anything else and I only get these thoughts when I'm spending time with her and I think about how much I love her. I am crying now because I just had the thought and I get scared because I feel like if I'm thinking it so frequently that it's going to happen. I've never had intrusive thoughts that centered around people other than myself and I don't know what to do. She is healthy and happy and so full of life. I have a brother as well and I don't have these sort of thoughts about him, but he is 12 years older than our sister and I am 4 years older than him. Christ, she's only 3. Iam aware everyone will die, but consistently having the thought daily that just my sister will die is messing with me so much. 

I can't handle this and I'm going to have my first anxiety attack in a while because of it. What is this?! Intuition, intrusive thought, anxiety?? Do you have ANY advice as to how to deal with this?