Don't know what to do... Can't stop thinking about death and dying

[Inigo]

If your dad hadn't been there at the time of the accident, I think you'd be in sorrow, and sad about your uncle's death. Since your dad was there, it's hitting way too close to home. Your parents are getting older and their mortality was brought home to you in a dramatic way. It's completely understandable for you to be so worried now.

I agree with everyone else that you need to find someone to talk to just to ease your mind. As time goes by, your fears should ease, but talking to someone might help them ease faster.