Self harm is a common thing. Can't say if it is getting more common in recent years or if it is merely getting more reported. However, I do not think there is a direct link between BDSM and self harm. While it is true that many self harmers turn to BDSM as a means of catharic release from thier troubles not all of them do this and not all BDSMers are former self harmers.

Also, some self harm is a cry for help rather than anything to do with the endorphins released by pain.

I suspect the psychology and physiology behind this is very complex and there are probably social elements as well...