When I go onto my friend's realm world, I go into the nether, with full iron armor, and go to kill some blazes for blaze rods. I kill some, take a few hits, about 3 hearts. Then the next few spawn in, take me to 6 hearts, I kill one, then just die. Instantly. It's happened multiple times, almost every time I go blaze farming, I die and it has nothing to do with me ignoring my health or anything. Just around half health to dead. There is a solution, though, which is using fire resistance potions. And this happens only on realms from what I've heard.