I saw my neighbors dog get hit by a car

A couple months ago I watched my next door neighbors dog run into the road and before I could even try to get her, it was too late. I still think about it often and cry every time I do. Is that normal? Obviously nobody is going to be happy directly after seeing that but I feel like it has effected me more deeply than it should have, especially since they are new neighbors so I don't even know them or their dog. A few years ago my dog was hit in the same spot on the same road so maybe that's why? I didn't actually witness it happening to my dog but I was the one who found him and it was too late to save him. And I think that I feel partly guilty because maybe if I had acted faster I could have saved their dog. Every time it crosses my mind it replays over and over in my head and it just makes me so sad.