It's officially the end of the expansion, because I'm tanking again. Every expansion, this happens. I start off tanking, something happens and I switch to DPS, and then by the end of the expansion I'm tanking again. The best part is that it usually happens in the middle of working on heroic progression, meaning that I'm suddenly tanking the hardest fights in the game. Usually without having ever tanked them before, in fact. Last night for instance I found out that I am much better at doing Heroic Norushen if I go down to kill the big add with some Vengeance built up, for how much it helps with Shield Barrier if I mis-time and get hit by the big attack.
My gear is adequate - about ilevel 566, with quite a few heroic pieces - but it's still a learning curve and one that's sometimes fairly hard to adjust to, and not just for me. This is a raid we've been clearing weekly, and suddenly here's a new tank who doesn't know what's going on as well as the previous tanks did. Combine that with my general sense of perfectionism (I do not like making even the most understandable mistake) and it can be pretty stressful.
But sometimes it's necessary -- your group has all the healers it needs, and you volunteer to DPS. You've been playing a hunter, now you're on your priest healing instead. (Hi, Final.) You're a tank but you're burned out and you need a change of pace. So, how can you deal with this, both as a player and as a group with a player switch? While I'm not pretending to having any sort of universal answer, here's a few things I've noticed.