Not sure why they said it was a rare case. It happens all the time. Mine happened the same way. I rode my bike 15 miles on a 100 degree day, came home and worked in the yard for a few hours. It was the heat and just overdoing it that triggered mine. I have had them twice years apart, both times in May the exact same weekend when it started to really get hot in TX. Mine never went above my mid section.
Good luck and wait it out.