What does “death hanging over” a person mean? ?

I've never heard that expression in the US.  We say "death warmed-over" to mean someone looks very ill.

Might mean they are worried about an error they made at work that others have not noticed yet but are bound to eventually notice. Example - that important document you inadvertently shredded.

I've never heard that expression in the US.  We say "death warmed-over" to mean someone looks very ill.

No, it means that they look as though they will die soon (they look unwell).  It does not have to be true that they are almost dead, but often that is the idea (they will die soon, almost certainly).

The saying could also be used to say that they appear to be thinking that their life is over or nearly so (are extremely unhappy), rather than said literally to mean that they are truly dying.

Usually when not meant literally (looks like they believe themselves to be dying rather than they look really sick and are close to death), the statement would be said hyperbolically, as a big exaggeration on purpose to make a point, when the person just looks really unhappy rather than actually and truly sick.  They look so unhappy that you are made to think that they must be dying because nothing else could be that bad.

No one would be so cruel as to tell the truly sick person that they look like death is hanging over them.  You can suppose that they are already aware of it.  You might say that to someone who just seems supremely unhappy, as a way to jar them into recognizing that it could actually be worse, they could actually be dying, so get some perspective here and lighten up.

It means that someone is speculating that the person may die soon. There are a couple of reasons for saying this.

1) That person is reckless and is putting their own life in danger. Maybe they drive too fast, are using drugs or are doing foolish things that may kill them.

2) That person is gravely ill and probably does not have much longer to live.

i dont think it means they'll die soon, they might just look like it

Yeah or they are close to it.