No it dosent have to hurt, i know of at least two babies who would feed beautifully, smile and coo happily, then vomit and hit the far wall with the feed they had just had, then contiue to smile beautifuuly. Unfortunatly, both my dc's had reflux where they rarely possited, never projectile vomited, and screamed for approx 20 out of 24 hrs.
Heres hoping no3 due in Jan dosent have it at all.