When it happens in mid-winter, as it does to my husband and to others who've described symptoms on this thread, it's likely not heat-induced.  In the cases of fever, nausea, chills, etc, it's a reaction to the toxins in whatever mold has infiltrated the grain.......corn, beans, rice, wheat, whatever, or a reaction to the dust from the grain itself. 

No doubt you've suffered after that heat exposure you mentioned, and were certainly sick, but it's a different situation than the sensitivity to mold or grain dust.