Rarely. Marathon training in summer, and being lazy about starting long runs early in the morning.

I'm pretty confident that I can say the incidence is not zero, but I'd agree it's less than 4.

this is over years. starting a multi hour run at 10 instead of 7 has some side effects. I'm not fast. I cover the distance. I've gotten into really weird headspace. I'm pretty good about tracking calories, so I'm pretty sure it was the heat from running when it's hot.

Heatwaves cause deaths and increased hospitalization at least in Europe. I presume it's not any better elsewhere.