There is the possibility of getting an orgasm because of fear or a shock. I know this because I have experienced this twice at school, once in a math exam and once while an exam of machine typing. It was not that pleasant but strange and embarassing and as I am male I had to hide the wet spot.

Researching the internet I have not found much material, some forum posts of a few girls who have experienced this once or twice, also during an exam.

Maybe the answer is the symathic nervous system which causes an orgasm but also the fight-and-flight response.

The only thing one can find are the videos of three orgasms in sling shot malta. The responses seem to be real orgasms.

If anyone knows a valid source for further research, please comment!

Edit: I finally found some hints how this might be possible.
The genital area has adrenaline-sensitive receptors. A quick release of adrenaline into the bloodstream will trigger the orgasm.