Heat and my body do not mix

The hot UK weather on Monday 11 July 2022 was not good for me and really messes my body. It’s very odd. When I was in the far-east in 2005 the hot humid weather was tolerable and did not affect me, yet over the last three or four years it almost knocks me flat. Now is that because I am older, or has the MS progression left me susceptible to heat. A question I do not know the answer.