You have it exactly right. That's the classic symptom of overreaching. The trick is to back off as soon as you start seeing that, before it becomes overtraining. Right now, I think you can easily recover. Just back off your weekday rides to Z1 and no more than 1 hr./day. I think you could still race once a week at this stage. Try that and see how it goes on your next race. If you're still bad, you might have to miss a weekend.