I have full marathon in 16days. I did the longest run last sunday following nice and easy recovery run. Then i suddely became ill, and haven't run for 5 days. I'm still feeling prettty fragile, so will not run for at least a day or two. What happens to my fitness after being ill? I 've been running 5,6 days a week until now, so i'm little worried that part of what i achieved during training will be lost?