I am stunned, I can't imagine the shock you must be feeling. I am so very sorry that you have to go through this.

***
When my cat, Billy, died unexpectedly last year, I phoned my vet. I had 3 options:
- do nothing and wonder forever
- attempt to get some answers via an organ review
- an organ review AND lab tests to possible find a reason (more expensive than the option above).

Please note that it is quite possible to do ALL of this and still never really know WHY.

I chose the organ review, and thankfully DID get some answers. I was mostly worried about something contagious which could be a risk for the other pets here. Those fears WERE allayed because the cause was found. Again, that may not be in every case.