Yeah that is it. I cannot regulate my body temp too well anymore. I overheat. My temperature goes up in heat. It will go up a half a degree if I take a long, hot shower or being out in ambient heat. If that happens, I am wrecked!! I have vertigo to the point of wall walking again, I am very fatigued, all my symptoms are magnified a ton. I will not feel better until my temp is back down for at leat 30 minutes.
I have all sorts of gadgets to help with this. I have two different types of cooling vests (one is evaporative the other is ice packs). I have cooling neck bands and hand held misters. I keep a close eye on the weather and humidity. I try to do everything in the cool of the morning during the summer.
Heat is very often a complaint of MSers. Here is a link for more info.
http://ms.about.com/od/signssymptoms/a/heat_intoleranc.htm