Tested in WoWScape
first you must have learned Ice Block Ice Block - Spells - World of Warcraft
next you need to be affected by dots (for ex. from ally warlock or priest) and when you have 1-3% cast Ice Block, you die but your corpse stay in ice block after spell expires you release spirit and after rezurect become immune to damage
p.s. i don't know why, fall dmg isn't immune