I am a trained and qualified hypnotist (stage and clinical) and have been practising formally and informally for just over ten years now. Autogenic training is something with which I am intimately familiar and unfortunately, the notion that you can somehow use it to commit suicide is a medical fallacy, a myth.
Suggestion and hypnosis can and do allow you to accomplish a physical effect on your body, this is exactly why placebos work, but it is simply not possible to use suggestion and essentially 'will' yourself to stop your heart. You can slow your heart-rate down through focused relaxation techniques; I've learned to do this myself over the years, but any mechanism by which this could possibly lead to suicide would be purely coincidental and likely predicated and attributed to an underlying condition (in my professional, albeit non-medical opinion).
Not wishing to challenge anybody's beliefs here, but it's probably worth mentioning that I have taken part in experiments in which I have induced everything from 'astral projection' to a 'near-death experience' to past life regression in multiple subjects with little more than psychological suggestion. Again, not to discredit anybody's beliefs and say that these things don't exist, but these experiences were all attributable to hallucinations, false memories and altered states of consciousness.
Hypnosis (such as autogenic training) can easily be used to produce a hallucination that has all of the properties of a classic "near-death experience" (bright white light, floating above body, being aware of conversations in the room whilst asleep, strong emotions, religious/spiritual imagery etc), but there is a world of difference between producing such phenomena and actually "willing oneself to death".
I'm happy to get into the technical debate if anybody disagrees, but personally I would advise being very, very wary of anybody proclaiming that any form of hypnosis is capable of causing death, or indeed any of the other popular myths like hypnotic mind-control or hypnotised assassins or seducing people into bed using hypnosis etc.