Overtraining and functional overreaching aren't the same thing
The term 'overtraining' gets used far more loosely in the fitness world than in sports science, which distinguishes several degrees of excess load with different consequences. Functional overreaching — a short-term, often deliberate push beyond normal load (a hard training block before a competition, say), followed by a planned reduction in volume — is actually a useful training strategy: a temporary performance dip gets followed by supercompensation and a rise above baseline once recovery happens.
Actual overtraining is something else entirely: a state of chronic excess stress without adequate recovery, stretched over weeks or months, leading to a persistent performance decline, sleep disruption, mood changes, and hormonal disturbances that don't bounce back after a few days off — they require weeks or even months of genuinely reduced load to resolve.
The key practical difference is how quickly you recover. If a couple of easier days bring performance back to normal, that was functional overreaching — a normal part of the training process. If fatigue and reduced performance persist for weeks despite rest, that signals a much more serious problem requiring a significantly longer and more deliberate reduction in load.