Hi Diana, I own a FIR (Far-Infrared-Sauna) sauna and love it. My family and I have only had good experience with it and only felt better! I would recommend starting out slowly, only 30 minutes as you suggested, as you may have detoxed a little rapidly with your first session. It feels great to know you are getting rid of all those toxins!
As to the heat concern FIR (Far-Infrared-Sauna) saunas are much less heat than even conventional saunas, so this is just a ploy by those in high places to keep people from healing themselves. I even have no problem saunaing for 30 minutes when I am pregnant till the last trimester, then it feels to warm for me and I obey my bodies signal and resume sauna use once again after baby arrives.
There was a time when no matter what I tried (and I tried a lot!) I was not sweating in the sauna, as it turned out I was low on electrolites and possibly trace minerals. I started putting a half a teaspoon of celtic Sea Salt (not the stuff you buy in the grocery store, REAL Sea Salt ) in a quart of water and drinking it each day as well as juicing some carrots and Celery together. I think I was low on sodium as I juice carrots quite frequently, but it needed the addition of a bit of Celery for balance. The Sea Salt provides quite a few trace minterals so this could have been it as well. In any rate, I started sweating once again very well in just a matter of a few days!! In less than 10 minutes usually. My husband sweats much quicker, just within minutes, but his metabolism is super high--lucky duck. Enjoy your FIR (Far-Infrared-Sauna) experience, they are so healthful for you! Caitlin Lorraine