Seems a majority of people are confidently blaming it on the hit he got on the tackle, even though it looked relatively typical and ordinary. That even though this sort of thing has basically never happened before.
I wouldn't have expected this event to result in a suspended NFL game, or get the media attention it has. But obviously it will take something significant to force attention to this issue.
That it was right after a tackle like that supports this medical explanation. Still, it would seem if this is so easily explained like that, there would be far more cases of this happening in the NFL world. The hit/tackle didn't seem out of the ordinary.