I may be exaggerating somewhat for dramatic effect (pretentious? moi?), though if it's really hot I am noticeably dopey. So far it hasn't seemed worthwhile to do anything more than stoic endurance, given that my bit of the UK is typically only that hot for a few days at a time, a couple of times a year, and effective fitting of aircon would require significant engineering. If the frequency or duration of really hot weather changes, I might have to re-evaluate that.
In the meantime... win!