training for marathon, my second with first last year. Did well last year except for leg cramps at 20 mi. this year I have good long runs, last being 18 mi, but during my two mi walk I need to sit down as feeling a bit faint, and ill. After getting home and showing I had to sit for a while mid drying off. I felt bad for a couple hours. This pattern has repeated for all runs over 13 mi.