As I can remember,Moriarty was using info against Sherlock from Mycroft,right?So maybe the Fall was planned from Moriarty,Mycroft and Sherlock too.That's how Sherlock was sure for his jump and...Moriarty's suicide!!!Sherlock was "surprised" and acted as he had to,in order to play the game...and save his friends!Moriarty was satisfied that the game was on,plus he had a "nice fellow", (Mycroft)...Mycroft may needed Moriarty alive so he helped him with his suicide"!!!And Sherlock wouldn't be so "actor" before he jumps.Maybe he knows the Moriarty's trick from Mycroft and has to be emotional in order to fool Moriarty! After all, "This is a magic trick..."

Of course,he could be shot from a sniper in the back of his head as I didn't see any serious injuries in the front of his face.And this would destroy my previous theory...