Feel your pain
I ran over my own cat in May. My husband and I were leaving for a belated honeymoon. Our beloved adopted kitty, Thomas, had been following us around all day - he'd even been sleeping in my car. I had lost another cat 8 months earlier, and the irony was that I had just realized that week Thomas had been helping me get over the loss of the other. He proved his amazing-ness every day after bringing him home from the shelter as a sociable, funny two-year old cat.
But that day, it was as though he knew we were going to leave him. Before making one last errand, I looked out at my car and saw him sleeping under it, and he looked up at me that moment. Despite the fact I saw him, I got distracted and ran to get an item from my room, came back, and started the car and put it in reverse, excited to be on vacation.
The dreaded bump that happened a split second later immediately baffled me. "What was that?!?!" Now, it is burned in my memory as the most awful sensation I've had in my life. Then I saw him run out from under the car - his back sunken. He managed to leap a 6 foot fence into our backyard. I ran inside through the house, out to the back to find him on the side of the house, gasping and convulsing. I scooped him up, and tore through the house back to my car - in a complete state of chaotic angst. I got back in the driver seat, with him convulsing in my lap. In ten seconds, he went limp. I began to howl in my car. Trying to dial my husband on a touch screen phone was a nightmare... my stuttering fingers wouldn't let me dial.
I am comforted to know that you are all out there, sharing in the grief and guilt of this horrible event. The only thing that brings me comfort is a belief in the fact that he may be still out in the spirit-sphere, and a hope that he knows I am sorry and would reverse it if I could. I truly hope to see him again - rainbow bridge or wherever he went in that split second.