No damage in survival after dying

I was in the nether fighting a whiter skeleton to where it got me low health so i kill it whilst having the wither effect and i quickly change the gamemode back to peaceful but the game said i died in the chat but my character was still moving and all my loot was dropped when you die but i didn't lose any xp. I return to the overworld to where i find out i cant take damage no matter what if its by drowning or fall damage or by and iron golem i couldn't die.