I had the same kind of letter Maria and it is a very distressing thing to read. My dear husband hated going to the doctor and it grieved me so much when I was told there would be a post mortem. I felt that they were investigating me because he'd had a tummy upset the night before he died, did they think I'd poisoned him? For heavens sake!!!
Everything came back clear though although the post mortem delayed the funeral for weeks, it seemed heartless at the time.
I feel for you Maria. All I can offer you is the hope that when all the tests are done and you get the results you will have peace of mind in knowing that he was well cared for in the process and you will know for sure what caused his death.