Oo, totally normal po yan! Most newborns sleep with their mouths open kasi ang kanilang breathing ay mas nakatuon sa nose pa lang, at sobrang baba ng muscle tone nila pa, kaya natural lang na bumubukas ang bibig. A few of us moms in our group were worried about this din when our babies were newborns, pero the pedia assured us it's just part of their development at babalik normal na yan as they grow. Walang problema yan, pero lang if may signs of difficulty breathing or parang struggling siya, then check with your doctor na.