I'm having a break from running and I've come to the conclusion that I get trashed if I do multiple workouts in one week.
I followed the NSM as closely as I could. For example I had averaged ~ 5:40 for 5k and I was doing 10x3 minutes at 6:10 or 3x10 minutes at 6:25. I got more and more tired and I wasn't even running 7 days a week. I tried slowing things down, so I did 5x6 minutes at 6:20 but my race results were poor.
So I'm not sure how to train now except to focus on quality once a week.