Well indeed it might be a fine line at times but to my way of thinking
those that meditated excessively were likely trying to use it to
suppress emotions, or it should demonstrate the effect of their
miasmatic background (sycotic excess?) This would fall into the
category of not being well prior to the practice (ooops I mean
'discipline

) in my book. I too know some that overdid it, but none
that got ill from it, except those that over-fasted , or had too
zealous an adherence to the brown rice diet!
In my experience those that go off the rails ( i.e. for whom the
discipline is harmful were only those that you wouldn't have said were
OK in the first place. As far as I can guage this applies to the
examples you give . I have also said in another post that a teacher IS
required. As far as getting messed up with drugs, natural or not, that
is a completely separate subject!

.
I see what you say about something's naturalness not equating to
safeness, and agree in most instances, however I'm not so sure when it
comes to spiritual discipline, unless the discipline itself is
unnatural (some are!:-)). No doubt some teachers have interesting
techniques not to be embarked upon but by the most courageous, but
whether it will give the the result they seek only their heart can
judge.
Simon