Your remaining HP (if any) is displayed after all the monsters have attacked. If you still live, you can look at your HP remaining and make a decision (aka the 'Fight or Flight Reflex') whether to attempt to Attack again, or to Run away. If you think your HP level is too low, then you'd better run.

When you die during a multi-attack, you can be sure that your HP dropped to (or below) zero, so you're dead for the day, no reason to display your current HP.

If you're really desperate to see your HP after being killed, you can look yourself up in the high score list.