For me, it just hits when I get hot. It could be that I'm exerting myself, the room gets hot, or even if I get nervous or stressed. So perhaps it would be more accurate to say that it comes whenever I start to sweat. I only have visuals signs, like redness, when it gets really bad. The worst episode I've had was during our company chili cook-off a few weeks ago. The room was packed, it was already hot in there, and then I went and ate something called Chernobyl Chili. *Facepalm* I had about 10 minutes of excruciating pain across my entire body, and it wasn't cold outside that day so I couldn't even escape the building for relief.
I've also found that I can make it worse by losing control of my emotions when it happens. Sometimes I get so pissed off and frustrated because it hurts pretty bad, and that creates a downward spiral and makes it hurt worse. If I can take some deep breaths and try to stay calm through the worst of the pain, it usually doesn't get unbearable.
Thanks for that link. I'm going to check it out.