"My baby was sleeping so well...what happened??" Sound familiar? We hear this all. the. time. Our answers vary, depending on the unique baby in question - in our experience, the answer can be anything from teething to illness to temperament to birth of a new sibling to nap transition. But often, our answer is - sleep regression. Generally, we offer up a diagnosis of sleep regression for babies and toddlers who are the following ages: 4 months (read about the 4 month sleep