Thanks for your help mrsD.
I'll pursue the B12/folic acid angle.

I eat pretty healthy, certainly not too much salt and almost never any snack food like chips. I do have the occassional Chinese buffet so I'm getting some MSG. My blood pressure is a little on the low side.

I don't take any acid lowering drugs but I did just start taking a vitamin D. I had probably taken one/day for 3 days by the time I had the B complex reaction.