Obsessive and Dark Daydreams?

Ever since I was 13 I fantasized about bad things happening to me, either a bad illness or a bad physical injury from some sort of accident.
I don't even know if "fantasized" is the right word, because I don't actually want these things to happen. I day dream about it constantly every day. Nothing bad ever happened in my life and I don't struggle with any sort of depression.

I don't know why I obsessively think about it every day, even going as far as learning about illness and injuries to make sure I'm accurate.

I don't think this is normal and I'm afraid of telling anyone about it. Why do I do this?
Obsessive and Dark Daydreams?
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