That sounds like heat exhaustion. From many years at Pennsic I learned to recognize it. One day in the first aid tent all I got was heat stuff and one ankle cut. Remedies: get in the shade or better yet AC if possible, get into a COOL (not cold) shower; pack wet cloths on head and under arms (helps cool core in a hurry) and drink tepid water. The headache is probably from dehydration. Half strength Gatorade, tepid, went down really well for the folks, too.

Heat stroke is extremely dangerous! You stop sweating and your body starts to cook. This is what happened to Vikings nose tackle Korey Stringer.