I plan and lead a 2 week trip in the Rockies yearly. Last Summer we were in Rocky Mtn N.P., at els of 11 to 13.5k. I'd spent the better part of a few weeks figuring meals, water availability, escape routes, etc., and we had myself and the SO flying out, meeting up with 4 others, and starting. Two days prior to departure I come down with what I'm certain is bronchitis.
Go to the walk-in clinic the day before, and I've got bronchitis, an upper respiratory infection, and a sinus infection (some kinda hat trick, huh!). Was prescribed 500mg. of Biaxin (IIRC it was 2x/day, but might've been only once....was still more than enough, either way).
So we fly in to Denver, spend a day at my brothers to begin acclimatizing, and start the next day. I've never been in such a bad way on the trail, and was really second guessing my decision. I was so weak setting up camp was terribly laborsome, and was worried about my strength in the event of an accident (as I never guide people to a locale I'm not 100% I can get them back out of...this facet of the trip really plagued me, and I broke down on a quiet section of the trail for a few mins, away from the eyes and ears of those I was with). The first 2-3 days were uber-tough, but the antibiotic started to take effect and I was 80% for the remainder, and we all had a great time. I honestly think I'd have been better off staying home that trip, but then I'd have missed out on some great memories/times with loved ones that I'll always cherish.