When you suddenly lose concentration and randomly come to think about something related to World of Warcraft, it's probably time to take a break from the game.
In my case I was once in a music festival with my gang. We had already drank loads of tequila shots and were having a good time together until a sitting group of foreign people made eye contact with us and started to shout us to come closer. My friend told me to ignore them and avoid fights since the police was patrolling the area. Until I felt a can hit me behind my head and I suddenly thought "What would Saurfang do?" out of nowhere. And yes, I turned while they were distracted laughing, picked up a chair and cleaved them. Rest of the night was spent behind bars.
Another one was when I was getting satisfied by my girlfriend and suddenly I thought "Hm, wonder what my guild is doing. I hope the tanking shield from Karazhan didn't drop." After that I took a half year break from WoW, since it was the first time I couldn't control my thoughts.
Tell me about yours!