Stop if you feel faint or pain!

"Stop if you feel faint or pain" is an example of syllepsis:

A figure of speech in which one word simultaneously modifies two or more other words such that the modification must be understood differently with respect to each modified word; often causing humorous incongruity.

The syllepsis section of wikipedia's zeugma article includes numerous examples of several forms. Both of your suggested revisions correctly improve upon the original wording.

I agree: the sentence is awkward because it's imposing double-duty on a word.

I came across a deliberate example like this once in a humor book. It went something like, "On the one hand, Dr Shickley is a careful and thorough researcher. On the other hand he wears a ring."