We're doing some confirmation testing right now, but here's all the requirements we know about Living Dead

You must receive heals equal to your total HP amount. (10,000 HP needs 10,000 points of healing)
Benediction alone does not work. Over heals do not count, so a Benediction will restore 100% -1 HP. You need to then take damage and heal up via a healer, self healing, or the natural HP tick.