First thing I would say that babies of that age are highly vulnerable to accidents and there must be someone to monitor there activities and keep a watch round the clock till they are of 2years atleast.
From a flat fall on chest sometimes can lead to a contusion/bruise
in lung tissue or a small rent there to lead to pneumothorax; although rare in babies due to resilient bones and cartilages- But if occurs will limit the childs activities by increased breathlessness due to inability to supply oxygen
I would suggest a Chest Xray.
If that's OK then no cause of worry but.......
....Take care in future!