i dunno what it could be exactly, one thing to look at though is how much an how hard you cough from holding it in or the size hit you take.. ive noticed the same thing but usually only when i hold a oversized hit over my limit and cough my ass off ill have the sweats.. also when i quit for a while to lower my tolerance and its like a first time high again my face, cheecks and forehead get warm when im high..