I don't know about you, but I've woken up in the middle of the night, on more than one occasion, from a terrible nightmare. I'm not talking about the Emerald Nightmare, you'll have to read Stormrage or talk to some tree-hugging druid if you want to hear about that. I'm referring to something similar to Argent Confessor Paletress' Confess attack; nightmares with a far more sinister source: memories of failed encounters from the past.
My guild's first attempt on the Twin Val'kyr has caused me more sleepless nights than any other so far. It was early in the week of their release, and so nobody in the raid had ever seen the Twins before. With no prior knowledge, we pulled the bosses blindly. My co-healer, a resto shaman, disconnected immediately due to an unknown problem. Suddenly I was faced with 10 targets all taking damage from a passive AoE aura, two tanks that were being hit pretty decently themselves, and random DPS in the group losing large chunks of their life at what seemed to be random times as balls of energy bounced around the room. This is my nightmare: the entire raid is on fire at once, and I'm all alone.