I keep imagining my mum dying

Im 22, and my mum is 59. We've not always had the most consistently good relationship, but when it all boils down to it, I absoloutely adore her and I know she loves me. She's gotten a lot softer as she's gotten older, and still at my big age, I still give her a big hug and tell her I love her before bed, go shopping with her, and all the stuff I think you're meant to grow out of. Recently I keep getting really vivid visions of her dying. I keep imagining being next to her hospital bed while she's flatlining, or having to go and see her in the morgue and stuff like that and it fucking kills me. As I'm typing this I'm crying so hard it's making me heave but I don't know how to make the thoughts stop. I know that probably, eventually, I'll have to navigate the world without my mummy, but right now I just want her to be alive and well, and I need these thoughts to stop but I don't know how