Curse of Vitality

• WWizards of the Coast2017-08-25
  Official Ruling
  Each Curse’s ability triggers only once, no matter how many creatures are attacking the enchanted player.
• WWizards of the Coast2017-08-25
  Official Ruling
  A player is attacking another player if they control a creature that’s attacking that player. If no creatures are attacking the enchanted player as a Curse’s ability resolves (most likely because they’ve left the battlefield), only the Curse’s controller performs its actions.
• WWizards of the Coast2017-08-25
  Official Ruling
  If you enchant yourself with one of these Curses, you’ll get its effects whenever another player attacks you.
• WWizards of the Coast2017-08-25
  Official Ruling
  The triggered ability of these Curses won’t trigger if only a planeswalker controlled by the enchanted player is attacked.

Rulings via Scryfall