I hope Zack is feeling better now.  All I can think of is that there was some
environmental factor which affected him en route to grandmothers (excluding the
possibility he ate some crumb somewhere?).  Along the lines of the diesel
exposure, I recently saw a program where a latex allergy could be greatly
magnified by the person eating banana or kiwi close to the time of exposure.
These contain enzymes that somehow exacerbate the reaction.

I too would have of course given the epipen. It was even my understanding,
that this type of treatment is useful even for non-allergic severe asthma
attacks (I was given adrenaline once in a clinic for bronchitis related asthma,
for instance).

With a 2 year old here at home severely allergic to eggs, grains, all nuts,
soy and innumerable other things, my heart goes out to you.  Take care.
I know this may be impossible but is there anyway you can get 911 access for
your home?

Susan.