What diseases scares you the most?

Hi to you all  

I'm new to this forum and I created my profile because I have a question for you. I do not have a child myself yet but many mums I speak to are very worried about their children, which got me thinking.

Last time your child was sick, what disease did you fear the most? What were you most scared of?

I know it's a scary question. It would help me a lot to understand though 

Thanks, 
Hansen