A planned dip versus a chronic hole
Functional overreaching is a deliberate, short-term increase in training stress that temporarily drops performance, followed by a planned reduction in load. After the lighter period the body rebounds above where it started, a rebound sometimes called supercompensation. Overtraining syndrome is the failure mode at the other end: a prolonged decline in performance and wellbeing that does not resolve with normal short rest and can take weeks or months to recover from.
Between them sits non-functional overreaching, where the dip lasts longer than intended and the rebound does not arrive on schedule.
Reading the warning signs honestly
The difference between a useful overload and a damaging one is largely about duration and recovery. Persistent fatigue, declining performance despite rest, disturbed sleep, mood changes, and elevated resting effort can signal that overreaching has tipped toward overtraining. Because the markers overlap with other medical conditions, they should not be self-diagnosed.
This is general educational information, not medical advice. If symptoms of overtraining or unexplained chronic fatigue persist, consult a qualified healthcare professional rather than simply training through it.