What Causes Dizziness, Double Vision And Headache After Doing Exercise?

my 17 y.o. son, very athletic, 185 lbs. 6'2" came home from working with trainer; was lightheaded, double vision, tingling & numbness in right hand, and headache behind his forehead. Unusually tired. Had hydrated well, and eaten carbs. and an apple pre-workout. takes no supplements. workout was 90 mins - warm up, some running, squats & weights, etc. all of which he's done before - frequently. -- in excellent general health. ? any ideas?