Heat Intolerance prevents the body from cooling a person's core body causing them symptoms that include foggy thinking, headaches, nausea and fatigue. Along with flares of symptoms of their disease like numbness and tingling.
These symptoms can be mild or severe and can be directly related to the temperature you are exposed to and the duration of exposure. The symptoms purportedly disappear once a person is out of the heat. I have found relief getting out of the heat, but it takes as much as 4 hours, a cool shower and a few cold drinks to get back to normal.