Kuma Hontosha

This isn't the only occurrences where dying in your dreams has lead to real life deaths. There have been a number of cases of somewhat similar but more rare diseases people are born with that have led to a few hundred deaths per year where the body actually has asphyxiated in the REM sleep in someone's sleeping patterns that had the same brain patterns as someone who has died in there sleep. Most people scientifically that have read the data have concluded to this being likely that these people died in their dream. While this is still currently being studied, it has been becoming steadily more common in recent years, and there is still no real treatment to prevent this from claiming more lives.