I wouldn't worry too much about the coach. You know best how you feel and you can adjust your workouts accordingly! Every now and then you end up with a bad set. I had a horrible hill repeat the other day. My body just didn't get into it and I was bonking too. You will come back another day and kick butt!
Thanks. It's funny how it can be so frustrating when a coach seems to think they know your body better than you. I am all for a little push to get faster, but sometimes the body just can't handle it. Goodluck this weekend!