The rosters are run super tight. You will be required to perform over time regularly. It is unlikely that you can change shifts as there is no one available to change with, so you will miss every major event in your marriage, children or social life unless you know it is coming 18 month is advance and can apply for leave. As far as I know leave planning is rolling and requires 18 month notice because there is not enough staff.
The fatigue comes from rotating rosters like doing a 6am start, finishing work at 1300 and returning to work at 2300 for a night shift. This is legal, I have personally done it many times. It is ok for the first night, but then when you do 0600-1300, 2300-0600 the same night, then again 2200-0600, you will be like a zombie.
You don't realize the level of fatigue until you stop doing it.