I dont quite understand your concern as the most critical info is missing from your post - what happened after you reached the early breakaway? If I'm decoding correctly, you say you didnt feel good and had low HR during power levels that shouldnt be an issue for you, but what happened next is what matters most. Sometimes after a big effort or feeling poorly something snaps and all of a sudden I'm fast, other times, not so much.
Bad days usually have a reason, when folks cant figure it out, they just say the ubiquitous "bad day". Could be just about anything, fatigue, which could be indicated by low HR (you've done lots of crits lately iirc, this takes a toll and eventually your body is going to slide off the top form); could be that you're getting a cold/sick (myself right now, horrible feeling and low Ws on last tuesday a.m. workout, sick by the p.m.); maybe you psyched yourself out since you were placing high priorty on this race? Maybe you were just in over your head. I highly doubt it's because you had to get out of bed and race earlier than normal - we're talking 9 a.m., not exactly the middle of the night.