You don't have to be able to do it (you can't). But if you try to do it, you will concentrate on each nostril in turn and little else, in synchronisation with

You don't have to be able to do it (you can't). But if you try to do it, you will concentrate on each nostril in turn and little else, in synchronisation with your breathing, which leads to the kind of mild auto-hypnosis that the GP is talking about.