All the time? No, but it’s happened before. Particularly with high neck manipulations that sever the spinal cord above the point where the nerves that control autonomic functions branch off from the neck (I think that’s C2?) Randomly? Also no. It’s a very predictable result of spinal manipulation. Just like lung cancer doesn’t happen ‘randomly’; if you smoke enough and long enough, it’s pretty likely, but if you don’t smoke at all it’s very, very rare.