The rear naked choke has long been considered a dangerous move in martial arts and MMA. In fact, only wrestling of the sports entertainment variety allows the move. Most fighting promotions and academies would never allow a student to hold the move for that long without checking on the other guy.
A recent video popped up on social media, showing an instructor applying the RNC. Unfortunately, things take a turn for the worse when the student begins convulsing because of the move. Watch this video of an instructor rear naked choke a student and cause a seizure