I suppose I'll have to refer to the Hodge's Harbrace when I get home
to check the legitimacy of your "an hilarious" construction. I can do
that in an hour, I think, over lunch. I don't know why I don't keep a
"Harbrace" here at the office. Perhaps, it's that you're falling back
on more esoteric usage to help 'clear' the air. I can appreciate
that.
--
Esoteric? Those of us of a certain age who actually studied English
formally learned that in speech "an" was used before a word beginning
with an "h" if the first syllable of that word was unstressed. The first
syllable of "hilarious" is unstressed. Another example, perhaps more
familiar: "An" historian.
Surely your English language complicator/mixmaster "knows" that.