How exactly do you distinguish between a 'profound altered state' and a 'mystical state'? - The 'profound alteration of consciousness' just IS the mystical state. The recent study by Roland Griffiths confirmed this: http://www.hopkinsmedicine.org/bin/s/m/ ... ocybin.pdf psilocybin typically causes fully mystical experiences
There is a big difference between a profound altered state and a mystical experience. Just remember all those train wreck stories on Erowid. You cannot dose someone and expect them to have a mystical experience on command, that's the point I wanted to make.
Maybe I should have said that without somekind of framework for the experience to happen in, it's merely a profound enhancement of perception (instead of alteration of consciousness, it's semantics but anyway ) most of the time. Surely some people that take psychedelics casually are presented with a full blown mystical experience but it's not guaranteed. I've talked to people that have had six hour episodes of full blown paranoia, trying to stop one of their friends killing himself by jumping in front of a train. No one died that night and all the ego's survived as well
My point about the knowledge of the shamen from the Amazon is that (as you said) they have indeed knowledge of these altered states and usually are trained in them. It's not unheard of that these people live solitary for a year in the jungle with the only contact they have, with their trainer. It's also not for nothing that these people often spend over a month drinking Ayahuasca daily to learn.
I don't know if deep states are available via yoga or meditation but I know for sure, that you don't either. I suspect it's very well possible under the right circumstances but I wouldn't bet my life on it.