I feel that pain. Like losing family.
I know what was worse for me was the feeling I somehow betrayed her.
I've heard it said that when our pets are ready they let us know, I know I had started to get the feeling it was her time months prior to the seizure. Still a hard thing to do, but it's much better than watching them suffer in pain.
Here we are 4 years later, I've thought about getting another dog, but there will never be a replacement for Knuckle-dog. (cross between a Knucklehead and a dog), that's what I called her. Sharp Pei Manchester Terrier mix.