my head was above the lava, water directly on top of a lava source forms obsidian. obsidian should have formed and the lava damage plus me holding spacebar should have rocketed me up through the obsidian, putting me out and ending the damage. the damage continued because lag prevented the water from turning the lava into obsidian, and I instantly went from ~6 hearts to dead. Obsidian will form when you're standing inside of it.