Comment by Tor3

Don't "tough it out" in a sauna. Stay until it feels uncomfortable, or, if you're not sure, keep track of your heart rate and get out if it increases too much. You'll get used to the sauna after frequenting it for some time, which usually results in being able to stay longer before it feels uncomfortable. Your ability to sweat will improve, for example, including being able to sweat on body parts where you may initially be unable to (it took a long time before my wife's calves "learned" to sweat, for example).