 [ Symptoms ] my 9 month old baby is coughing really hard while sleeping [ Disease ] your baby either has a cold viral infection or is teething or both babies often have a difficult time dealing with drainage either saliva or mucous when they are lying flat so a cough is important to clear their airway coughing can certainly be a sign of something more serious bronchiolitis rsv pneumonia etc  because your baby is immunocompromised due to age so it would be best to have a medical provider listen to those little lungs there is very little you can do at this age to control a cough but you can make it easier for them to swallow excess mucous by using a cool mist humidifier in the room and sucking out nasal mucous using a special bulb syringe a drop of saline in each nostril just prior to aspirating it will help loosen any thick mucous