Hi thanks for your question.
The bump which your son got following a trauma to his head could be haematoma
(collection of blood under skin.or a fracture
of mastoid bone (ear bone ).Nausea and ear pain
6 hours after head trauma
should not be taken lightly.It could be simply due to disturbence in the internal ear but could alos be due to more complex reasons like bleeding inside brain or fracture of mastoid bone.You may need CT scan head to rule out above mentioned reasons.Visit to ER is advisible.
Hope this answers your question.