Crying is a natural reaction.
I remember attending an RTC a few years ago when a bloke came off his motorbike and I was in the back of the ambulance with him and a paramedic.
He was holding my hand and slipped under, his eyes rolling back and his grip loosening and me and the paramedic worked on him until we got to the hospital where a med team took over. He died a short time later and when I got told I broke down in tears because I didn't save his life. I felt awful but also felt better for the release.
Firstly, agree totally with Sponge - some of the sights you guys see in the course of your job must be absolutely horrific ... I suppose you do learn to cope with it eventually, but you'd be inhuman for it not to get to you at all. Massive, massive respect.
Lots of things make me well up - the Royal Wedding on Friday for instance, purely because it reminded me of my own, albeit more modest, wedding day, but that was obviously a happiness thing rather than any kind of negative emotion - but there's only a few things that reduce me to a blubbering mess these days.
My wife (or girlfriend as she was at that point) still recalls the first time I cried in front of her - we'd been together several months by that time and she said she was honoured that I felt comfortable enough in our relationship that I could show that side of my character.
For me, music is also incredibly powerful. The last time I really bawled, the music I was listening to was what sealed the deal. It was a horrible time in our family: I was writing a eulogy for my dad's funeral - barely six months after my grandad had also died.
Given the situation, my choice of music was odd, to say the least - the soundtrack to Gladiator. I was typing out my eulogy on the computer and my eyes were filling up - basically it got to the track 'Honour Him' and the enormity of what I was doing and the circumstances just hit me and despite being a grown man in my mid-thirties, I cried like a child.
I'll say this though - it was better than any therapy. One big outpouring of emotion gave me sufficient mental strength to get through the funeral in one piece, although I had a bit of a wobble when I looked round and saw how many of Dad's old workmates from 30-40 years ago had turned up. I remember feeling deeply proud that they thought enough of him to take the time, some of them having travelled long distances to do so.
Oddly, I find crying is like throwing up when you're ill - in almost every case, I always feel so much better afterwards