I also occassionally get near the point of tears at work just from sheer frustration and stress, during an especially chaotic night. I also cry at home every couple of weeks or months after a build-up of "sadnesses" due to deaths, suffering patients and families, poor prognoses, etc. that are typical on a Med/Surg floor.
Around 3 months ago, though, I cried at work for the first time in many years. Without going into details, suffice it to say it'd been a particularly rough 3-11 shift, but I had a 90 year old man for a patient who was one of the loveliest, sweetest people I've ever cared for-- always appreciative, smiling, and a twinkle in his eyes. It was 10:30 and I hadn't had a chance to tape report, was still far from being caught up with charting and was upset from the frantic pace, so I was going to ask another nurse to bring this man his sleeping pill and cough medicine. But, everyone else was busy, so I decided to do it myself so I could say goodnight to the patient. As I gave him his meds. and wished him goodnight, he took my hands in his and said, "You're such a good nurse; you care so much and I want you to know that you're in the right profession." I smiled back at him as the tears were beginning to pool in my eyes and said, "You don't know how much that means to hear that tonight."
I hugged him, and ran to the staff bathroom to bawl my eyes out. I turned on the water in the sink full force so no one would hear my blubbering and didn't realize through my tears that the sink was overflowing. Then I started laughing at the puddle of water on the floor and my wet scrub top where I'd been leaning against the sink. Then I cried a little more, mopped up, and gave report to night shift.