From the writers of Grey's Anatomy on last night's episode:
The nice thing about having a big cast is that you get to mix and match the characters in a hundred different ways. You don’t often get to see Derek and Cristina together in a story line – they’re not tremendously fond of each other – but she did save his life. We hadn’t played any of the fallout from that yet this season. We got our chance to do so in this episode and it made me wonder why the heck we don’t have these two actors together more often. Patrick and Sandra were FANTASTIC together. Of course, the sad part of the story was that despite Derek’s best intentions, Cristina is nowhere near healed. At this point she might, in fact, be the biggest freak at Seattle Grace. Her PTSD is crippling. The question remains --will she ever come back from what happened?