do you have a fascination with vanpire movies? have you ever bit anyone before?
i was diagnosis with chronic depression, being depressed your thoughts are negative, so when i get a negative thought in my head. i tell myself something positive.
it's just like telling yourself you are beautiful in the mirror every morning.
this is just one suggestion of many.
for example when you get the urge to do it, tell yourself "you cant do that b/c it would hurt the person".