User blog comment:Smijes08/Giles' Death/@comment-2094142-20120822210054

You raise an excellent point; there really ought to be an article on this wiki that explains the difference between natural and mystical deaths.

Personally, what I think the writers mean with mystical death is any cause of death which cannot be described by contemporary medical science. In the case of Giles the cause of death was a broken neck, whether it was broken by a super-powered possesed vampire, a burglar, or an unlucky step on the stairs is irrelevant in my opinion.