I see you r from the. UK.It doesn't normally get hot there, does it? Here in Dallas, Tx, it really does. There r a few things that make one more intolerant of heat. If you are not aclimatized, by living in a generally cooler environment, it can take a whole season. If one is hyperthyroid or has suffered Heat Exhaustion or Heat Stroke, you can have heat intollerance. Also, the older we get, our bodies become less efficient at coolin.