Hi Rob. A lot of people have have itching of their head when hot, and sweating. I have never known anyone to develop a rash from it, so maybe you should see a Dermatologist. If all other causes are ruled out by the Dermatologist, then you may want to see a psychiatrist to determine if it is anxiety related. From what you wrote, the first time this rash appeared you began to worry over it. One thing about anxiety is the more you worry about something, the worse the anxiety gets. Anxiety alone will make us hot or sweat, so getting the anxiety under control may help a lot. You're not having an anxiety attack as we know it, but it's very possible that obcessing over this happening is making it worse, this leads to more anxiety and thus the vicious cycle. See a Dermatologist and go from there, I think you will get relief from him/her. Take care!