The Middle Ages

They often didn't! Those that did became acclimatised.

We didn't even have central heating until autumn 2010, and before that it was a little difficult at times But you do harden yourself up to it.

Many people would struggle a bit with an indoor temperature of 15 Celsius. But I just put on extra clothing and get on with the rest of my day.

Either that or control your body's temperature to accept cold weather.

For example, cold showers can be a bit hard to deal with at first but once you get used to it, just as normal as warm/hot water.

Plus, there are advantages to cold showers @ https://www.organicfacts.net/cold-showers.html

Everyone learns to adapt to their environment. I would say our ancestors were better at using their natural survival instincts than we are