Board Thread:General Discussion/@comment-84.202.176.245-20130901154231/@comment-6881629-20130901165343

If you have the Legendary edition you should have Dawnguard and that should have stopped npc's attacking full un-feed Vampires.

Without Dawnguard if a Vampire player doesn't feed after four days you will get attacked. Reload a save if you can before he attacked you (or escape and feed), find a sleeping npc sneak up activate them and select feed then npc's won't attack you for another four days.