Hi, I have a friend with a 5 week old baby and recently she has begun shaking the baby to settle her. It's not a violent shake, it's more of an agressive rock but it does make me a little concerned. The baby's head does bounce around a little. So my question is how much shaking is too much? The baby does settle after she's been rocked this way but I wonder if it's because she's received some kind of brain damage???