Why heavy singles feel different to recover from
Lifting near a one-rep max places a large demand on the nervous system, since maximal force requires near-complete motor-unit recruitment and high firing rates. The fatigue that follows such efforts is often described as central or neural, and anecdotally and in some research it can linger longer than the local muscle soreness from lighter, higher-rep work. This is why a true max-effort day is frequently programmed with more recovery around it.
By contrast, high-repetition training tends to produce fatigue that is more local to the muscles worked and clears on a more familiar timescale.
Interpreting the recovery window cautiously
The idea that very heavy lifts deplete the central nervous system for a day or more is a useful planning heuristic, but the exact mechanisms and durations are debated, and not all post-max tiredness is purely neural; muscle and connective tissue damage and general systemic stress all contribute. Recovery time varies with the lifter's training age, total volume, sleep, and stress.
This is general educational information, not individualized programming or medical advice. Persistent heavy fatigue warrants attention to recovery and, if needed, a professional.