don't laugh, but are you a coffee drinker? if so, do you consume the same amount of caffeine when you ride as you would on days you don't ride? I had a client who would suffer caffeine withdrawal symptoms after 3-4 hours on the bike. we added in some caffeine and all was good.

btw, I'm also doing Cycle Oregon. maybe we'll meet among the 2,000-odd cyclists?

Lorri