D.H.
D. ~
My niece did this exact thing. She would be running around playing, then all of a sudden say she didn't feel well, and then almost immediately throw up. The pediatrician told her mom that it was migraines! Apparently this is a typical sign of migraines in young children. You need to try to get him to realize what he's feeling a little sooner so you can medicate him in time. You can give him tylenol or motrin, a cool cloth to the head or neck, and a dark room - it should help.
good luck!
D.