I'm so sorry
Are you going to have a necropsy done? I don't know if I'd ever trust that friend again, as I have doubts about a little dog being able to run so fast and hard as to give himself a fatal brain injury. An injury, yes, but fatal? That just doesn't seem right to me. It would help to get a medical opinion one way or the other.
Again, I am so so very sorry for the loss of your little one
