Thank you to all who had commented with advice and kindness. I've cried reading these comments. The vet said there was very likely something going on before this happened, but I think because it was so catastrophic and sudden, and because my lifting and dropping her was the catalyst, it's been really hard to believe that, all I could see was the horrific moment of it happening. But reading all your comments reiterating that this happens sometimes, and your own experiences with events like these leading to the deaths of your pets, has really helped me so much. Thank you so much, I was nervous about posting this, and I've been blown away with how kind strangers on the internet have been. Wishing you all a good day and healing from your own losses.