We purchased a fixer-upper cabin in Big Bear, CA- altitude about 7000 ft. We have been going there almost every weekend to work on the place. Day one- I am fine, energetic, bike riding -with a bit windedness due to altitude. Day 2 every weekend except 1st, -nausea, headache, needing to urinate and bowel movements very often (not diarrhea), extreme fatigue. continues on the 2 hour drive home, Once home, I usually feel better, or go to sleep for an hour or so, and start feeling OK. Can t figure out the cause. any ideas?