Your clearly missing my point, Derren Brown is a showman, who uses a good knowledge of physiology to achive such things as this. He is in no way a Martial Artists or such, and is not selling such things as a 'technique' to defend yourself with. But comming from him I think its an interesting insight into how such things 'work' (even in a controlled enviroment a grown man is still collapsing against his will) and I just thought this might answer some questions as to how its done. I'm in no way saying it would work in a self-defence situation, I don't beleive it would in the slightest but I'm still interested in how it can be demonstarted at all.
"The deeper you delve into philosophy the sadder you become."