I'm leveling up resto staff right now to try out force siphon. Seems sweet but I'm wondering how often can it proc? I know shades (Nightblade skill)can make it proc, but is it any time you do damage to the target or is it each separate attack? For example, I'm fighting a boss and I use force siphon. Then I drop Veil of Blades on him which dies damage every .5 seconds. Will I be healed by it every. 5 seconds or just when I drop Veil?