My 16 year old son often suffers from a sudden onset headache, nausea, and goes very pale when he is outside on a warm day. It doesn t take long 15-45 minutes will do it. His headache is bad enough that he will go to bed and stay there for 3-4 hours or sometimes go to bed in the early evening and not get up until the morning. Are there any conditions that make a person overheat easily. The rest of the family will be outside the same amount of time with absolutely no ill effects. I am constantly on him to drink water because I know that this sounds like dehydration but I don t believe that to be the case.