I sometimes get into situations where I am being hit/damaged frequently but looking at my heal bar, it is at 50% aprox. but then I die. I look at the health bar and it is still at 50% but the actual health value is at 0 ???
This doesn't happen often but in a 6 hours period (was off,

I think it is beause the actual health value is being updated alot faster then the heal progress bar.
For me it is faster to look a the progress bar then the actual value.