The HP cost and increase of cost on this ability is way, WAY, WAAAYYYYYYY too high. 10% increase would make this viable with careful management, but 20% is just ridiculous unless you build like a tank, which entirely defeats the purpose in PVE...
As it is, with the self-healing only AND HP recovery nerf stacked on top, this ability is just as, or even more likely to kill you than aid you. At the VERY least, you could add an auto toggle off when you hit a low HP threshold as the toggle itself coupled with server lag makes it VERY unreliable with toggling on and off.