It works both ways IME. Sometimes I surprise myself with unexpected energy/strength, and sometimes I’m bitterly disappointed by my lack of performance. Often it’s in complete contradiction to what I expected. According to my GP it’s all very normal and common, and there is often absolutely no logical explanation. Although in your case, as suggested, I suspect that rest played an important part.
Having said that, I can’t remember what programme I saw on the telly last week, but they did a experiment where a doctor had one of his arms put in a plaster cast for a week (there was nothing wrong with his arm) After a week the cast was removed and he had apparently lost an inch in the circumference of his arm because of muscle loss due to immobility. Although I did find some aspects of the experiment rather unscientific.