If your child is vomiting every night, you should seek medical attention. If it isn't as often, but still regular you should still talk to a pediatrician about it.
Around 9 months, Mason started vomiting at night on a semi-regular basis. Every few months (longest was 6 months, shortest was 2 weeks) he would wake up in the middle of the night and would start vomiting every hour. This would continue until mid-morning where he would make a full recovery and eat enough for a small army. Apart from the vomiting, he showed no symptoms of being ill. We charted his foods to check for allergies, and found nothing. I spoke with 3 pediatricians and they all brushed me off. The process continued for 3 YEARS (!!!!) with nobody believing me that it was happening. About a year ago, I took him in to a pediatrician for another cause and it was a different doctor than we normally see. I mentioned it to her and she finally gave us the referral to a gastrointestinal doctor. The gastro doctor informed us it could be a few different things, the most likely of which is cyclical vomiting - something most children grow out of around 5-6 years old. It could also be an issue with his intestines where they didn't fully form correctly and are twisting on themselves when they get backed up - and then everything has to empty out so they are able to untwist! At our most recent appointment with the gastro specialist, we were given some forms to take in to the hospital during Mason's next episode so they could run tests on the vomit to see if it was a problem with his intestine. Wouldn't you know that appointment was 7 months ago, and he hasn't had an episode since (knock on wood) so although I was told to hold onto the forms, the doctor told me it is/was most likely cyclical vomiting.