Unless you have an necropsy or autopsy done on the animal, you
can't say it was from no apparent cause. You may NOT have SEEN a
reason, but there usually is one a vet can see. It could have had a
bacterial or virul infection. The diet could have been wrong, it
could have been genetic .... there is no way to tell unless you
have a vet involved. It may seem to some to be wasteful to have a
vet look at a dead animal, but it really isn't.
If you have other pets in the house or just yourself, you want
to rule out disease especially zoonotic ones (ones that can be
transmitted to humans). You should also have all animals checked
within a short (less then a week) time from getting it- if it was
free, from a petshop, you found it-- it doesn't matter... have it
check checked out.
Sorry to hear your rabbit passed.
I agree with the response above. Also: Rabbits from pet stores tend
to come from breeders or bunny 'farms' and are often inbred and
removed from their mother way too early. As an aside editorial
comment, it is best to get a rabbit from a local shelter or rescue
rather than a pet store. A rescue will (generally) have much more
knowledge about their particular rabbits and can provide you with
their background and health information (again, generally, but not