This does not sound like a "natural death" to me!
Pop eye is not a disease, just a symptom of the
final stages of some internal infection that ends
in the death of the fish. Labored breathing
usually indicates gill parasites or water problems
(high nitrites or other toxins). I don't know what
the cause is in your case. With Rams, the best
prevention is a month or 2 in quarantine at temps
in the mid 80s F (low 30s C), lots of clean water,
quality food - and hope for the best.