Whoa I had one of these! Mine took the form of a stroke due to occurring in the vertebral artery in my neck. Most are believed to be due to injury, often minor, plus bad luck. The chest ones are apparently often weightlifters who banged the bar on their chests the wrong way. No one who treated me had heard of a re-occurrence. The only well-known example we could find was the Australian national cricket player who died immediately after taking a knock to the head just below his helmet.