Should've posted this way earlier. This would be for 1.12.2 + newer versions. Anyway...

You know how the Hunger Bar jitters when it starts to drain and it increases in strength as it lowers further and further? I wonder if something like that can apply for Health. For example...

Between 100% to 50% Health, no jitter occurs however once you are at 50% or less health, the Hearts starts to jitter with it increasing in strength as you health lowers further and further.

The percentage value for when the health starts to jitter could be configurable, where at 0.5 the hearts will jitter if at 50% or less health, at 0.2 the hearts will jitter if at 20% or less health, much like if you had 4/20 health vanilla-wise.

Currently by default, hearts will only jitter if at 4 or less health no matter what.