Like Peter Borst I am also peanut allergic, and recently became allergic to
bees (after many stings, suddenly one "got" me with a big systemic reaction).

One factor besides swelling and breathing difficulties I feel I should
mention is blood pressure collapse.  When a severe allergic reaction gets
going, the capillaries all open up and your blood pressure plummets.
Epinephrine is a powerful vasoconstrictor that counteracts this.  Very low
blood pressure is as serious as breathing problems and can kill you too-
this is the "shock" component of anaphylactic shock reactions. A sting-ee
can be breathing just fine and suddenly pass out.

A side effect of the suddenly lowered BP is the lack of blood to the brain,
which makes thinking and planning difficult.  This is why the EpiPen is
replacing the AnaKit, you just have to push it into your thigh.

An Epipen is a good thing to keep around if you have bees.  I would use it
on someone with breathing problems or sudden dizziness or light-headedness,
including, now, me!