Must have been a dark runes then
He just timed it at the same time I got hit by a big shadow damage hit I guess lol.
Warlocks can life tap/hellfire out of it though.
The warriors and mages who should be your main offense should be preventing anyone from getting too close to healers, and should be the ones taking rocket helms. They can zerker rage or ice block it, or the priest, who should be way in the back can dispel it.
If a priest or shaman got hit by it, consider whether it was preventable. Did the healer get too close? Or could the warriors/mages do a better job peeling/blocking next time? Sometimes it’s impossible to prevent though and a priest just has to sit it. That’s where you need communicate, and have people blow big cooldowns like Nature’s Swiftness, Arcane Power, Recklessness, etc. to even the odds. If you have the luxury of 2 priests in one fight, they should be looking out for each other and instantly dispelling anything like this.