[The Saucepan Man]

One thing bothers me about Elvish "immortality", though.

It is said that they can die as a result of a physical assault, for example in combat. But they are immune from disease. And yet all diseases involve physical trauma of some kind. Viruses, bacteria and malignant growths all cause physical damage to the body, just like a blow from a sword does. What is it, I wonder, that makes them immune to internal assault, when they are vulnerable to external attack?

Psychological disorders are perhaps in a different category, and yet one form of psychological stress is fatal to Elves. They are prone to die from great sadness. Why so?

I know that I'm just being pernickety here and that I should simply suspend belief. But any theories?