Does the amount of dmg total collapse do to u vary?

In sandbox with chant and without chsnt it did like 3k+ dmg to me and with domain wihtout chant it did 4k+, but for some reason it somtimes just insta kills me, my hp is mostly at 9k or 7k most of the time but this one time i was doing dailies and popped a domain against 4 curse users and chanted my max, it insta killed me at 7k hp so is there like some mech or smth on this?