Hi,
I am a long time lurker and have had the same problem as Todd is experiencing.
The solution for me was fairly simple.  I just make sure that whatever greens
and salad makins I eat are organic and/or are thoroughly washed.  I suspect that
pesticide residues are producing the symptoms.  Also,  whenever I eat the
prepackaged lettuce (and often this is what is served in many eateries) I have a
more immediate reaction.  I wonder if added sulfites may exacerbate the problem.

Back to lurk mode,
Cindy