Andy has a lot of knowledge yes, no doubt about that.
Headaches from the sauna, yes... at first, but only marginal, and mostly if you overdo your session. If headache starts to develope, then end the session.. or take a break in a cold to lukewarm shower for 5-15 minutes, whatever...
There is diffrence and variations from person to person, yes. clearly.
I spend about 1.5hrs to 2hrs, but last time i went i did 2hrs but could tollerate 3, but i was getting bored... Ofcourse i don't stay in for such a long time in one go.. I do small go's for 4-8 minutes, then shower for 5, and reenter the sauna again, does that for 4-5 times or so then drinks half a liter of water, and takes a break for 10 minutes or so, then sauna more.. until the 1-1.5 or 2hrs has gone, ofcourse, the total time of 2hrs is not a nailed number, but as long as you feel is safe for you.... you will know, headache etc...... or simply by the feeling that you have had enough for the day....
Unpoisonous materials.... thats a luxury i cant be bothered with when doing sauna in public, but it IS in my mind... atleast it was in my mind....
My mind today, the gain is higher (sweat) than the re-uptake of poison from the materials in the sauna... so...... can't be too picky, because then one cant get nothing done....
Same with food.... processed food.... i know EVERYTHING is poisonous, but i have to eat, after all.... so i marginalise it.... not dropping it fully... same with sauna materials...... i choose not to think about it no more....
especially as the saunas help as much as they do... for me..

The conclusion about the sequence for parasite cleanse, kidneys and liver...
Read the Hulda book, The cure for all diseases!

And read from other sources on the net about Hulda's methods and ways...
DMSA scares the cra....p out of me.... from what i have read, to be honest!
and so does ala, also cillantro and chlorella...
I got burnt by chlorella badly a year ago.... am well today.... thanks to saunas... and more... cillantro however... i tried 3mnts ago... got back my back pain after just a little cillantro in soup, got rid of it again with more sauna later...
Oxygen.... i know nothing about that....
Mercury is not hard to meassure.... if the established medical profession really wanted to.... it wouldn't take a long time for them to pull a method out of their hats to meassure merc in a satisfying way! I'm sure of that...... corrupt medical establishment, saying its psycho somatic and anxst....... my god... how much i hate THEM...... and avoid them!
My attitude btw... is all natural... atleast that is for now... for me....
What comes later i cant tell now...

Get your self a copy of the Hulda books! They are as gold worth as Andy's book!