if you have to let him go for his sake, that takes courage and love on your part. I know how hard that dicision is, I had to have a young cat pts years some ago.
only 5 yeas old, that is very hard, I am so sorry for your grief.
as for the autopsy, contact the nearest university, or ask your vet about it,sometimes universities will do autopsies for less because they learn from it.
I know that is a morbid thought, but if you can learn what happened to him, maybe it is something to consider.
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