The human engine is not really an engine as we think of mechanical devices. Machines exhibit similar performance day after day with some degradation due to wear and need of maintenance. There is not fatigue or emotional factor in mechanical systems and mechanical systems do not get sick.

Human performance just varies and it is due to many factors. My performance can vary a lot and many times it is mental and has nothing to do with physiology.

IMO, the most likely reason is that you had a bad day, not enough sleep that is due to the previous night before the night of the event (not the night before the event), getting sick or mentally, not just in the game.

Overtraining is due to getting the body’s normal function way out of balance. If you are overtrained, recovery will not occur in a couple of days.

In general, most athletes that race their bikes get a 6 month window of training and performance gains. After six months, a break is needed. That is why many start serious training in February and race through August. They hit August ripping the pedals off the bike and want to keep racing. The reality is that they need a break. If one wants a longer season then a mid summer break is in order.

I suggest taking a couple of days off and if you have not had a rest week in several months, then take a week off and do a couple of recovery rides. Rest is not the enemy.