Although I cannot answer this as a pro, I can try to give you some insight about what may be challanging. My sister is a nurse, and she tends to tell horror stories about how she has to pick up the slack from the other shifts of nurses. For instance, there was a patient of hers that had just had major surgery, and during the night she became unresponsive (around 4 am), when my sister came in at 7am, the night nurse had told her that the patient was unresponsive, so my sister asked "Did you call the doctor", the nurse stated she had done nothing, basically just leaving the patient alone. My sister rushed into the room, started to shake her a little to see if maybe she was in a deep sleep, but still no response (remember this is now 3 hours after she became unresponsive) so my sister called the DR, and boy did she hear a mouth full from him, he stated "why didn't anyone call me?". To make a long story short, she had an anerisim (spelling
sorry) in the brain and caused to her to basically bleed to death, she died later that day. The thing that was upsetting to my sister is that she had to listen to the DR vent every frustration he had out on her, although she did everything she should have done right!! I'm sure that can be extrellemy frustrating.
Some other things may be like the ungrateful or unstable patients, you could have some that spit on you, yell at you, possibly try to inflict some type of bodily harm, those could make it very stressful as well!!
You have to remember you are putting your life on the line for these people, you could very easily contract some type of deadly disease if your not careful.
But there are many aspects to nursing that can make it challanging, and I only speak of what I have heard, I am not a nurse yet, but someday hope to.