If your baby falls back on a soft surface like a bed or cot mattress then this unlikely to be more than a superficial issue which causes discomfort. However, if your baby falls back on a hard surface this can range from a bruise, cut or even brain damage. Most doctors will advise that if the baby is fine and alert after banging their head then things should be fine. Just monitor for a few days. The signs of something more serious are vomiting, drowsy, irritable, eating less, or having trouble using a part of their body. If one or more of these symptoms is evident then seek medical attention straight away.