Limbs feel heavy, but then rejuvenated. Hearts feel heavy, but then are lifted. Rapid breathing calms, racing hearts still, scratches and bruises no longer impede.the narrative the there must be some in-fiction indication of missing HP or otherwise there is no in-character justification for use of HP replenishing things. There must also be some in-character understanding of how these HP restoring things help.
I think LotR (both book and film) exemplifies ways to think about this.