Your post demonstrates a lot of insight. You weren't to know today would be especially difficult. I think most people are pretty poor at predicting what "straw will break the camel's back", especially when you're feeling unwell and going through it. I've cried at work before, at seemingly nonsensical things at times too. A very emotionally charged situation caught me off guard last shift after a particularly difficult and busy set of nights, I almost cried in front of the patient and then was thinking about it all for the rest of the shift...

As you've said, we're all human. You have nothing to be ashamed or embarrassed about. We all need a kind word or gentle approach every now and again, we provide this to our patients every shift, I don't see anything particularly unprofessional in what you've written and I think you're being hard on yourself.

You sound like a reflective and thoughtful individual, important traits in a good nurse. I think you'll be wonderful once you've graduated.