My 4 year old son is vomiting, but only at night. One night vomit at midnight, next night dry heaves again 'round midnight, next night vomit again but much earlier about 1 hour after being put to bed. He eats normal quantities of food during the day but is self limiting to water and cracker types of food and refuses dinner. Also he bounces around the house all day as though everyting is fine. What is going on?