When watching Napoleon Dynamite.

Or how about when eating a certain family member's cooking.
Ok seriously.
Physical
I took a nasty blow to the back of the head in high school and was spewing blood everywhere. I was in shock until they said they had called an ambulance, at which point the seriousness of the situation kinda hit me at once.
Emotional
The first week or so after getting dumped by my first g/f. I was completely out of my mind. Every time I thought about it I thought I was going to puke. A buddy of mine was going through the same thing, we got together and got drunk around a campfire. When I woke up, he had 3rd degree burns on his arm from when he fell and lay on a hot rock by the fire. His condition plus the real likelihood of getting busted for drinking didn't help. Also, the hangover afterward was intense. I can't ever remember going through so much pain in my life as I did at the start of coping with losing her. But I think for my friend it was far worse.
Oops
The first time I really screwed up at work and got a stern talking-to from my boss I was feeling pretty horrible. It would take too long to explain what I did wrong, but basically I presented some incorrect numbers based on a really dumb mistake. At the time I was responsible for supporting myself and my wife.
Car-Related
Spun out on a patch of ice, fishtailed, and put the car in a ditch. Though, it doesn't really count because the whole time I thought at any moment I would regain control, that is, until I was looking at clouds through the windshield.
Stress
Getting a job after graduating stressed the hell out of me. I was on a deadline to get a job due to my wife needing to send off a grad-school acceptance at university. It was a horrible time to be interviewing and I think I'd been through about 30 interviews without getting any follow-ups. Unbelievably stressful time. Worked out though.
And BlackZ is right, your g/f missing a period is not funny, not in the slightest.