This is just my idea since it seems some squishy DPS are saying they'll have a hard time keeping the skill toggled, so I've been theorizing why not make it drain the vampire timer instead? The ability does say it lets your hunger take hold so maybe having it drain a minute a second off the 4 hour timer is a good idea? Of course it should still have a debuff for the power it gives so obviously keep the part where only you can heal yourself. ((Or balance the spell/weapon damage off the different resource being drained))
When it comes to morphs the Simmering Frenzy morph would greatly increase this drain, or maybe even include the HP drain as well as the vampire stage drain. Would give players an even greater incentive to feed and would make it more accessible to the squishier classes to use, as well as making the vampire play style a bit more aggressive. Also wouldn't make it a death sentence to keep on in PVP which is going to have a 60% healing debuff placed on you on top of whatever things are going to be thrown your way.
PC NA - Ceyanna Ashton - Breton Vampire MagDK