That absorb health spell takes forever to kill anyone but the only other way to get perk points is to attack bite but i cant figure out how pleese help

I would like to know this to.

You have to get them low HP and then switch to melee combat in the VL form and do a Power attack, its random when it works.

The absorb spell is very strong, a bug exists that when serana as your follower the spell is weakened. You may be experiencing this.

You perform a bite attack randomly when you power attack at an enemy with low health.