As from my investigations, yes it can be dangerous BUT it is a VERY VERY small percentage. The ones who are more at risk are like 80 year olds with problems with blook flow. This can cause a stroke. The liklyhood of a younger person going through that is slim to none. It is not like in the movies when they show people breaking each others necks....not like that at all.
So yes there is a chance for stroke....but mostly in older people with zero history of going to a chiropractor and a history of circulatory problems. Hope this helps. :)