Searched couldnt find if you say this is a repost please post link.
Ok well I was at stormwind harbor and I jumped off the very top of the harbor to the bottom...This normally kills me
Well I did this by accident because I dont want to die so on my way down im like shit...in the same second i hit the ground i hit the deathknight ability Rune Tap and I survived. I had 1hp and I got the achivement.
I had 10,753 health at the time and my rune tab heals for 2366.
It might work with other classes instant self healing spells but as my own other char is a warlock with no heals I cannot test it.
Have fun
P.S. latency was 113ms