Instead of costing Health per second, Each second it is active should apply Heal Absorption to the user equal to the initial health cost of the ability while also allowing heals from teammates. Like so:

Major note before getting into it: The heal absorption is completely removed upon deactivation.

Blood Frenzy: Allow your monstrous appetites to take hold, increasing your Weapon and Spell Damage by [600 / 610 / 620 / 630]. While toggled on, You become afflicted with Heal Absorption every second, negating the next 1920 points of healing done and healing taken, the heal absorption strength increases by 20% each second. When you toggle this ability off, you heal for [27 / 28 / 29 / 30]% of the total Heal Absorption total afflicted on you after a 1 second delay*.

• Simmering Frenzy: Allow your monstrous appetites to take hold, increasing your Weapon and Spell Damage by [630 / 640 / 650 / 660]. While toggled on, You become afflicted with Heal Absorption every second, negating the next 1920 points of healing done and healing taken, the heal absorption strength increases by 20% and the Weapon and Spell Damage bonus increases by 8% every second. When you toggle this ability off, you heal for 30% of the total Heal Absorption total afflicted on you after a 1 second delay*.
• Sated Fury: Allow your monstrous appetites to take hold, increasing your Weapon and Spell Damage by 630. While toggled on, You become afflicted with Heal Absorption every second, negating the next 1920 points of healing done and healing taken, the heal absorption strength increases by 20% each second. When you toggle this ability off, you heal for 30% of the total Heal Absorption total afflicted on you after a 1 second delay* and gain a damage shield equal to 30% of the heal absorption removed on deactivation for [5/6/7/8]seconds.

(*the 1 second delay is so that upon deactivation, that the heal does not get simultaneously negated by the heal absorption as it would create a problem.)

I thought this idea should be brought to light (no pun intended) because for one, having an increasing health cost makes it too dangerous in a lot of situations, but if it was heal absorption equal to the total health cost of the ability (especially if it scales based on certain factors like vampire stage, cost reducing enchantments, sets, etc.) it may not be so dangerous but just as punishing.

Namely, using it would prevent you from healing yourself as effectively via heal absorption and becoming more and more powerful as it drags out, means that you would have to deactivate it at some point to try keep your health topped up against tougher adversaries, not to mention as heal absorption affects all self heals and heals from teammates, I figured why not allow teammates to heal you as well as yourself while active since the absorption scales higher the longer it is active. Not only would it encourage smarter play in a way especially for groups with dedicated healers, but if you get careless, your opponent could kill you before you even had a chance at healing due to the heal absorption factor.

Blood frenzy has the heal effect upon deactivation as a baseline function to allow some measure of delayed recovery equal to the amount of Heal absorption you have at the time of deactivation. Simmering frenzy has a lower increase in weapon and spell damage increase per second as it would result in more powerful heals based on that factor, while Sated Frenzy Provides a more Defensive Option based on the amount of heal absorption removed at the time of deactivation.

What are your thoughts on this? More importantly, any chance this could get reviewed by the Combat team for a potential future update @ZOS_Kevin?