Cause of death: Hemorrhage
When it happened: 964 AD
Where it happened: Rome

Apparently, Pope John XII wasn't a very good pope. In fact, he used to hit on women all the time, and when they rejected him, he would often force himself on them. There's a story out there that says Pope John XII actually died of a stroke while sleeping with a woman by the name of Stefanetta. What likely happened is that while the two were getting it on, Stefanetta's husband walked in on them and murdered Pope John XII on the spot.