This was only a problem for a couple weeks so we didn't consult a vet. In hindsight we should have, which makes us very upset.
So sorry for the sudden loss of your dog. It us especially hard when it is unexpected and we seem to have read a few of these posts recently. Unless a necropsy were done, there is no definitive answer any if us can give you. The lack of appetite and weight loss was most likely a sign that something was going on which could have been some issue with the intestines, liver, kidneys, or even a cancer. Did you ever consult a Vet?
Sometimes, we just never get a definite answer.
My condolences, no matter what "answers" you get you have still lost a loved pet, a hard fact of life for pet owners.
I don't have the numbers but I think it possible the dogs biological clock just ran out.. what is the life expectancy for the Labrador? I'll guess 9 to 12 years, making 9 early but not "unusual".
It could have been a stroke or heart attack if it happened suddenly. I really don't know and all any of us could offer is a guess.
Wishing you best and hope you'll consider taking in a rescue dog which may also help rescue you from your sorrow.