When you come off orientation, you're not expected to know everything. Your charge nurse and resource nurses will expect you to ask questions. If your patient is crashing, they will want to know about it.
At the beginning of your shift, take 5 minutes to think about worst case scenarios. What is the worst thing that could happen to your patient? What would the beginning signs of that look like? What would you do? If you are still on orientation, you need to ask your preceptor about worst case scenarios *now*. Review them with her for each patient. When something unusual or terrible happens on my unit, I still ask - how did you know it was happening? What were the early signs?
So when your patient takes a turn for the worse, don't panic, get a set of vitals while you're thinking about what could be happening. Think of urine output as a vital sign, too. Do you have protocols for standing orders? Know them cold when you come off orientation. Review what's going on with another nurse.