Looking back, I think I had more "bad days" when I was newer nurse. Until I figured out a good routine, how to prioritize, and time management.
Having said that though... every once in a while I still get run over by a tough shift now and again. Unfortunately, I don't know a single nurse working in a clinical position that doesn't encounter that now and again. It's a part of the nursing world.
First of all, see how the next shift goes. Then look back a week or so later. It that was just a "bad" shift, then you can be thankful that it was just that:) If you start to see a "pattern" of frequent bad shifts then may ask for assistance from a trusted co-worker or manager for suggestions. I also at one point realized I was "expecting" shift to be bad before I got to work... and you know what - those shifts often lived up to my negative expectations. I had to change my thinking, and suddenly I had less "bad" shifts.
Where I work now, it's a given Fridays will be a hot mess. We just roll with it and joke about it being Friday. Knowing this ahead of time makes it much easier to deal with. We help each other out as much as we can and know we will likely be sitting in a empty conference room having a "charting party" (not really a party, just nurses frantically charting so we can go home) after we give report. Often we will order a pizza to be delivered or someone will bring something that can be eaten quickly when people have a minute during the shift.
I make sure I start every shift with a full water bottle and there are always a few quick snacks in my work pouch - it's a zip top bag where I keep extra pens, highlighters, sharpie, ibuprofen, change for the vending machine, a flashlight, a mirror for assessing heels and my headlamp for catheter insertions:) Snacks that are non-perishable and have good energy value (individual packs of nuts, protein bar etc). Sometimes, taking 3 minutes for self care can end up saving me a time later if I have a minute to refuel and figure out a game plan (instead of just putting out little fires).
I have a 50 minute commute, I take that time to process a little and then listen to great music and enjoy the drive home. It took me a long time, but I've learned to (almost always) leave the day behind by the time I get home. I've got some co-workers who stop by the gym. Or Starbucks. Talk to your co-workers for suggestions on how they decompress after a crazy shift.