I actually had a pretty traumatizing emergency situation recently, with EMT training under my belt, and did not expect at all for how different a real life emergency situation feels. If it's a true emergency, it's going to be chaotic - I was never prepared for what it would be like for everything to happen so fast, and trying so hard not to let all my training go out the window.

Realize that you will need to keep a level head (as much as possible), and don't let your training (rules, procedures, protocols, what's the "best" thing to do) get in the way of what's in front of you. Sounds counterintuitive, but if you get caught up in the details of thinking what am I supposed to do - you forget to actually do, and some common sense goes out the window.