How Can Heat Strokes Causing Grand Mal Seizure Be Avoided?

I suffer from heat stroke complications... I had a gran mal seizure in '89 while working in a 140 degree room laying block(cement block)... Since then I must be very careful not to overheat... I am aware of the warning signs:I stop sweating I get goose bumps while I am extremely hot sometimes. In such cases I must get out of the heat and rehydrate. But in the past 2 weeks, I have been getting prickley pains all over my head and neck when I open the van door as the heat escapes... Even when I "precool" the van wAC... Is this another normal warniunf sign that I was unaware of? It is QUITE PAINFUL ! It stops soon after the van cools off and gets aired out... HELP !!