not sure what to title it: fall hacking?

sometimes in bgs i run into a fight and i have not been hit by a single spell. then BAM dead 12444 to the face. just says you have taken 12444 damage. no combat log specifics. this a hack or just a bug? the last time it happened it was with a blood elf mage ---------. i was fighting her in AB at the mine and once she got low iwas instantly hit for 12444 which was my max life at the time. she then proceeded to walk to flag and cap it, acted like nothing happened. anyone else experience this ?

Once i got hit for 3 or something k in AB moment gate on ally side opened.