While "Health Boost" effect is active and you take constant damage, example firedamage and the "helath boost" effect ends you take damage and "fake die". After pressing "respawn" you are there, where you "died" second ago. Also if you then look in the inventory you see yourself "dead". After that I tried to kill myself with The "/kill" command and it took 3-6 seconds and I died, but you can see that the health display says "2147483647" harts.