I'll have to admit, when I was still leveling up my healer, I was guilty of using the Regen at all times, even outside of battle. One of my friends brought it to my attention that it was why I was getting aggro during pulls. (I'm not entirely sure why I didn't catch on beforehand haha. I'm a bit derpy sometimes.) It took some time after that to get used to casting it at the right times. I only do it after all the mobs have been pulled and I get the tank up to a decent health, and then I refresh it until there are only a couple of enemies left. Then I just Cure the rest of the time. Sometimes I accidentally hit it though, but I usually ask the tank to remove it if that happens.