This is truly dependent on the type of nursing. I am in critical care and somedays are absolutely wonderful, other days you are racing against the clock to provide for your patients. Restless/ agitated or declining are usually the hardest to care for, because they are the most labor intensive. When a code is called (for whatever reason) your day is thrown off. In all honesty stress is very high in our job, but that is usually why we work 3-days a week so that we have enough off time to recuperate and take me-time. Never be afraid to ask for help!!!
As a physician and surgeon, the most difficult situations I’ve seen nurses in our during codes, where a patient is actively dying and needs resuscitation, and during rounds when they may be berated or belittled by physicians. The first can be a rush as you get better at it, and the second can be very demotivating.