When to use a and/or an?

I’m not referring to the rule that a and an are used, depending on the first letter of the word following being a vowel or a consonant.
But rather in a situation like the following (a sentence I just wrote in an answer in another thread).
Namely: ”...if it was a (health/life or death) emergency….”, is what I wrote, my reasoning being that the reader will probably read the health/life or death part immediately after the a part.
Or should I have used the an, because the main sentence is an emergency (which could be a health or a life or death one)?

Grammar grandma’s (or young men and women)???