It is still controversial but hypnotism is reasonaly well accepted as a genuine type of brain state.
No doubt there are people out there getting hypnotised in MRI machines and we will hear about it soon.
Having read Derron Brown's book and as a hypnotist 'hynotised' me once i'm fairly confident that it's not real. By real i mean that someone cannot simply be hypnotised into doing the bidding of others. Generally hynotism involves a lot of relaxation techniques and using participants who are willing the system to work.
It is also ridiculously easy for someone to become registered as a hymotiist so i'd say it's a long way off from becoming a fully accepted form of medical treatment or anything along those lines.