try opening to lan with commands on and type these three commands seperately:
/gamerule fireDamage true
/gamerule drowningDamage true
/gamerule fallDamage true
that should get all your damage back on.
Did you even read or watch the video? It's not a creeper or spider in the nether, that's what the death message says. It says you're killed by a spider when you're being hit by arrows, same goes with the creeper. Also it is completely invisible, not even visible in spectator mode.
yes im sorry, i couldnt find the search feature on the site at the time