I have a 3 year old son who has been perfectly fine during the day but for the past 5 nights has been vomiting a large vomit in his sleep. We will change him and put him back to bed and he will go back to sleep and be totally fine from then on eating and playing normally until he is bed again the next night and it happens again. There hasn't even been any complaining of a sore tummy even when he's vomitting. Any ideas what it could be?