A few years back I was having a strange back pain that would wake me up. It hurt inside, like on my ribcage inside but on the back. In the morning after I got up it would go away. The doctor did a thorough exam and said that there was nothing wrong with me. Then he wrote out on his Rx pad, Get more sleep, lose a little weight, exercise, and HAVE MORE FUN.
I showed the note to my wife. She refused to believe that the doctor was talking about the same sort of fun that I was thinking about. Her loss. I did everything on the list. No more back ache. No more stress. It was the HAVE MORE FUN part that did the most good.
With all of the research on the brain, and how orgasm releases endorphins and other natural chemicals on the brain, it does not surprise me at all. A lot of these hormones/endorphins etc are natural pain killers as well, and they all have a calming affect on the body. I wonder how much fun they had doing that research, or better yet, how much fun their "test" candidates had being guinea pigs!