As I understand it, a surprising number of people actually tie themselves up before hanging themselves, understanding that under reflex they'll try to claw their way free even though they want to die the time.
Not sure about the feet, but it's quite possible to tie yourself up, then if you use something thin for the rope and have a good drop(or just fat), decapitation is quite possible.
They go by the way the knots are tied, but it's not something they want to release to the public.