dear son did that when he was 9 month old. he also took a few small spoon of porridge/cereal and sealed his mouth. as for milk, he can dragged for 7 hr and only took around 120ml! we brought him to the pediatrician and he said cos his weight gain was too much (he was 11+kg then) and his body is sending 'signal' to tell him to stop taking in so much food/milk to slow down his weight gain. and true enough, after few weeks, his weight dropped abit and his appetite for milk gained back, then slowly gained back the solid food appetite.
as for your baby, it could be teething, or even throat infection. if he still drinks milk when he is hungry, lik 5-6hrs later, should be ok. but if he keep rejecting everything for many days, mayb you would want to bring him to pediatrician to check if it is throat infection =)